Kernel Tuning
Apr 24, 2009
as part of a project I have lately been looking into various aspects of kernel tuning. Most notably lately tuning the TCP stack for more efficient memory usage/throughput.
Thought I would start this thread to mention some of the tools I'd found for doing testing and see what anyone else had to recommend.
So far my favorite of the bunch is nuttcp. Its easy to use and gives a very good idea of how much of your bandwidth you are able to utilize.
A few interesting web pages are as follows for anyone interested in the topic:
[url]- Tuning TCP for High Bandwidth Delay networks
[url]- TCP Tuning Cook book, some interesting information in there as well
[url]...formanceTuning - Performance Tuning TWiki. Has a list of useful tools, flags for existing tools and ways to monitor network performance from a system level, along with some suggestions of things to correct
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Jun 7, 2009
Can anybody show me how to tune the prefork module I don't know where to begin.
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May 5, 2009
shared hosting env?
/etc/sysctl.conf:
vm.dirty_background_ratio = 20
vm.dirty_ratio = 60
blockdev --setra 16384 /dev/sda
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Apr 11, 2008
i have this couple of windows 2003 servers, colocated in data center, i need to improve download speeds to our customers who are at least 200ms away, the end user is not using download accelarator,
is there a way that any settings to be done on server so that per thread speed can be increased, this case the server and client both have the ability to make a connection at more than a megabit speed. i did some search but all the articles point to end user and not the server saying to increase tcp window size etc.. not sure if those articles relate to server side changes.
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Dec 19, 2008
I have Linux server with WHM/Cpanel with 2000 domains now my problem is.Mysql is using 90-100% CPU usage and 1500-2000 queries are running at a time so please guide me how can i optimize it and how can i tune mysql server so it doesn't go high.
I have configure my.cnf file as --->
max_allowed_packet = 4M
set-variable = max_connections=100
safe-show-database
query_cache_limit=1M
query_cache_size=128M
query_cache_type=1
key_buffer_size=256M
long_query_time = 3
table_cache=9092
how can i do this and any changes is require ?
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Apr 4, 2007
I've noticed I'm getting high numbers for Handler_read_rnd_next.
How can I dig deeper to find out which tables/queries are causing this?
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Jun 16, 2008
What have you found to be the best tuning sites for MySQL?
I'm getting into a bit of trouble. We have a weather site, and with all of the traffic, we're getting a little tapped out. When the loads hit between 134 and 160, the mail clients start to time out. Apache is still pretty fast, although it takes a little longer once you cross loads of 80, 5 second page loads, but when it hits between 130 and 160, I'm seeing 15-20 second page loads. DA is impossible above 80 but SSH is still very workable. Apache is tweaked to the max. I've kicked up some of the sizes in MySQL several weeks ago, and that did it them. However, we're taking on about 22,000 to 25,000 uniques an hour now. We normally can handle that no problem, but people are asking for maps a lot more now with the flooding and all. That requires a lot of MySQL lookups and the CPU creating a lot more maps. The maps I already cache for the duration, which is 15 minutes. The only horse I have left to whip is MySQL. After that, it will probably be a move to FreeBSD 7, but I'd like to throw in a few tweaks yet before we do that.
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Nov 22, 2007
Quote:
MySQL Version 4.1.22-standard i686
Uptime = 0 days 0 hrs 4 min 15 sec
Avg. qps = 17
Total Questions = 4479
Threads Connected = 1
Warning: Server has not been running for at least 48hrs.
It may not be safe to use these recommendations
To find out more information on how each of these
runtime variables effects performance visit:
[url]
SLOW QUERIES
Current long_query_time = 10 sec.
You have 1 out of 4491 that take longer than 10 sec. to complete
The slow query log is NOT enabled.
Your long_query_time may be too high, I typically set this under 5 sec.
WORKER THREADS
Current thread_cache_size = 128
Current threads_cached = 6
Current threads_per_sec = 0
Historic threads_per_sec = 0
Your thread_cache_size is fine
MAX CONNECTIONS
Current max_connections = 2000
Current threads_connected = 1
Historic max_used_connections = 7
The number of used connections is 0% of the configured maximum.
You are using less than 10% of your configured max_connections.
Lowering max_connections could help to avoid an over-allocation of memory
See "MEMORY USAGE" section to make sure you are not over-allocating
MEMORY USAGE
Max Memory Ever Allocated : 96 M
Configured Max Per-thread Buffers : 10 G
Configured Max Global Buffers : 58 M
Configured Max Memory Limit : 10 G
Total System Memory : 3.95 G
Max memory limit exceeds 85% of total system memory
KEY BUFFER
Current MyISAM index space = 78 M
Current key_buffer_size = 16 M
Key cache miss rate is 1 : 735
Key buffer fill ratio = 8.00 %
Your key_buffer_size seems to be too high.
Perhaps you can use these resources elsewhere
QUERY CACHE
Query cache is enabled
Current query_cache_size = 32 M
Current query_cache_used = 4 M
Current query_cach_limit = 1 M
Current Query cache fill ratio = 14.83 %
Your query_cache_size seems to be too high.
Perhaps you can use these resources elsewhere
MySQL won't cache query results that are larger than query_cache_limit in size
SORT OPERATIONS
Current sort_buffer_size = 2 M
Current record/read_rnd_buffer_size = 256 K
Sort buffer seems to be fine
JOINS
Current join_buffer_size = 1.00 M
You have had 0 queries where a join could not use an index properly
Your joins seem to be using indexes properly
OPEN FILES LIMIT
Current open_files_limit = 10000 files
The open_files_limit should typically be set to at least 2x-3x
that of table_cache if you have heavy MyISAM usage.
Your open_files_limit value seems to be fine
TABLE CACHE
Current table_cache value = 1024 tables
You have a total of 721 tables
You have 93 open tables.
The table_cache value seems to be fine
TEMP TABLES
Current max_heap_table_size = 16 M
Current tmp_table_size = 32 M
Of 212 temp tables, 0% were created on disk
Effective in-memory tmp_table_size is limited to max_heap_table_size.
Created disk tmp tables ratio seems fine
TABLE SCANS
Current read_buffer_size = 1 M
Current table scan ratio = 17754 : 1
You have a high ratio of sequential access requests to SELECTs
You may benefit from raising read_buffer_size and/or improving your use of indexes.
TABLE LOCKING
Current Lock Wait ratio = 1 : 76
You may benefit from selective use of InnoDB.
If you have long running SELECT's against MyISAM tables and perform
frequent updates consider setting 'low_priority_updates=1'
how to make the changes in red? My server works good for awhile, but then gets REALLY REALLY slow.
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Jul 13, 2009
I have a VPS system on the west coast of the US, and access it from the east coast. Sometimes I can get 1Mbyte/sec downloads, and other times it is as bad a 250KB/sec.
I have done some pings, and have not seen any packet loss. I've experimented with sysctl and changed some parameters to hopefully help, but really haven't seen much of a difference.
Does anyone have a recommendation as to what I could do different to squeeze a little more speed out of the connection? The problem is that from both sides of the US, I see ping times (depending on different ISPs on the east coast) from 80ms-120ms.
Here is what I've tuned so far:
kern.ipc.nmbclusters=65535
net.inet.tcp.sendbuf_max=16777216
net.inet.tcp.recvbuf_max=16777216
net.inet.tcp.sendspace=78840
net.inet.tcp.recvspace=78840
net.inet.tcp.mssdflt=1460
net.inet.tcp.slowstart_flightsize=52
net.inet.tcp.inflight.min=29200
net.inet.tcp.sendbuf_inc=8760
net.inet.tcp.recvbuf_inc=8760
net.inet.tcp.sendbuf_auto=1
net.inet.tcp.recvbuf_auto=1
net.inet.tcp.delayed_ack=1
net.inet.tcp.delacktime=150
net.inet.tcp.inflight.enable=1
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Mar 29, 2007
we have one box in hivelocity.net that has been down so many times this month that we were forced to remove links to siteuptime where we were once so proud of having a 99.7% uptime for 3 years in theplanet.
syslog shows that just before crashing, these entries were made:
kernel: kernel BUG at mm/rmap.c:479
kernel: invalid operand:0000 [#1]
dmesg also shows this:
...
Brought up 2 CPUs
zapping low mappings.
checking if image is initramfs... it is
Freeing initrd memory: 482k freed
NET: Registered protocol family 16
PCI: PCI BIOS revision 2.10 entry at 0xf9f20, last bus=1
PCI: Using configuration type 1
mtrr: v2.0 (20020519)
mtrr: your CPUs had inconsistent fixed MTRR settings
mtrr: probably your BIOS does not setup all CPUs.
mtrr: corrected configuration.
...
i've googled these messages and they point to ram problems.
hivelocity.net claims to have done diagnostics on the box and that there were no problems reported.
they said this is a result of a sys configuration problem made by us.
any ideas?
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May 20, 2009
running centos/virtuozzo 2.6.18-028stab062.3
when i configure vmware it asks at one point for kernel header files. where would i find them to match the current kernel?
i asked at parallels forums but help there is very scarce. i checked openVZ repositories and they dont yet have headers for this version.
what are my options? i have one last windows machine left and want to run it in VMware.
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Apr 29, 2007
Last year I ordered a new server with Centos 4.3 and it had the kernel kernel 2.6.9-34.0.2ELsmp installed. It runned fine and I didn't update any packages since then.
Today I started getting a problem where both mysqld and kswapd0 uses very high amounts of CPU, spiking up to 100% and my memory usage is at 99% all the time. The problem seems exactly the same as the one mentioned in this thread.
In that thread the exact same kernel is said to be insecure and to cause this problem. I also came across a centOS bug that reports this problem with high cpu, mem usage and mysql & kswapd0 consuming all resources.
In the linked thread the person solved the problem by upgrading to kernel 2.6.9-42 using rpms but others recommended a newer kernel or a custom compiled kernel for CentOS.
Apparently when they used yum it said 34.0.2 was the latest kernel.
What should I do to upgrade the kernel, which version should i upgrade to, and where do I get it from? I won't be able to compile a custom kernel and I've only installed basic rpm packages before.
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May 13, 2007
I am trying to install the kernel source.
I have downloaded kernel-2.6.20-1.2948.fc6.src.rpm
I am using fedora 6 64bit.
here are my current kernels:
kernel-headers-2.6.20-1.2948.fc6
kernel-devel-2.6.20-1.2944.fc6
yum-kernel-module-1.0.3-1.fc6
kernel-2.6.20-1.2944.fc6
kernel-devel-2.6.20-1.2948.fc6
kernel-2.6.20-1.2948.fc6
here is what I seen when I installed kernel-2.6.20-1.2948.fc6.src.rpm
rpm -ivh kernel-2.6.20-1.2948.fc6.src.rpm
1:kernel warning: user brewbuilder does not exist - using root
warning: group brewbuilder does not exist - using root
warning: user brewbuilder does not exist - using root
########################################### [100%]
warning: user brewbuilder does not exist - using root
warning: group brewbuilder does not exist - using root
then when I ran:
rpmbuild -bp --target=$(uname -m) /usr/src/redhat/SPECS/kernel-2.6.spec
I seen this error:
+ Arch=x86_64
+ make ARCH=x86_64 nonint_oldconfig
In file included from /usr/include/sys/socket.h:35,
from /usr/include/netinet/in.h:24,
from /usr/include/arpa/inet.h:23,
from scripts/basic/fixdep.c:117:
/usr/include/bits/socket.h:310:24: error: asm/socket.h: No such file or directory
make[1]: *** [scripts/basic/fixdep] Error 1
make: *** [scripts_basic] Error 2
error: Bad exit status from /var/tmp/rpm-tmp.93770 (%prep)
I need to have this installed to get a app installed etc...
suggestions or ideas?
thanks
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Apr 4, 2009
I have a Xen VPS. I started with a Debian 4 image and have since upgraded to Debian 5. Firstly was this advisable? Secondly what Kernel version should I be running, or rather is it set by my installation or by the Xen server?
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Feb 15, 2007
Does it take 2 hours to have a new kernel up and running? The tech is taking forever to finish.
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Aug 4, 2009
What is the best way to find out which filesystems and harddrive drivers you can remove? Obviously, i need ext2,3 but how do you find which HD you only need?
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Jun 15, 2009
recently,my dedicated server down frequently,
i can not find any important info from /var/log/messages
but i find some records many time on it,those like
----------------------------------
Jun 15 05:30:40 server kernel: ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jun 15 05:30:40 server kernel: ata1.00: (irq_stat 0x40000001)
Jun 15 05:30:40 server kernel: ata1.00: cmd 25/00:08:42:23:d2/00:00:2c:00:00/e0 tag 0 cdb 0x0 data 4096 in
Jun 15 05:30:40 server kernel: res 51/40:00:42:23:d2/00:00:2c:00:00/e0 Emask 0x9 (media error)
Jun 15 05:30:40 server kernel: ata1.00: configured for UDMA/133
Jun 15 05:30:40 server kernel: ata1: EH complete
Jun 15 05:30:42 server kernel: ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jun 15 05:30:42 server kernel: ata1.00: (irq_stat 0x40000001)
Jun 15 05:30:42 server kernel: ata1.00: cmd 25/00:08:42:23:d2/00:00:2c:00:00/e0 tag 0 cdb 0x0 data 4096 in
Jun 15 05:30:42 server kernel: res 51/40:00:42:23:d2/00:00:2c:00:00/e0 Emask 0x9 (media error)
Jun 15 05:30:42 server kernel: ata1.00: configured for UDMA/133
Jun 15 05:30:42 server kernel: ata1: EH complete
Jun 15 05:30:44 server kernel: ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jun 15 05:30:51 server kernel: ata1.00: (irq_stat 0x40000001)
Jun 15 05:30:51 server kernel: ata1.00: cmd 25/00:08:42:23:d2/00:00:2c:00:00/e0 tag 0 cdb 0x0 data 4096 in
Jun 15 05:30:51 server kernel: res 51/40:00:42:23:d2/00:00:2c:00:00/e0 Emask 0x9 (media error)
Jun 15 05:30:51 server kernel: ata1.00: configured for UDMA/133
Jun 15 05:30:51 server kernel: ata1: EH complete
Jun 15 05:30:51 server kernel: ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jun 15 05:30:51 server kernel: ata1.00: (irq_stat 0x40000001)
Jun 15 05:30:51 server kernel: ata1.00: cmd 25/00:08:42:23:d2/00:00:2c:00:00/e0 tag 0 cdb 0x0 data 4096 in
Jun 15 05:30:51 server kernel: res 51/40:00:42:23:d2/00:00:2c:00:00/e0 Emask 0x9 (media error)
Jun 15 05:30:51 server kernel: ata1.00: configured for UDMA/133
Jun 15 05:30:51 server kernel: ata1: EH complete
Jun 15 05:30:51 server kernel: ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jun 15 05:30:51 server kernel: ata1.00: (irq_stat 0x40000001)
Jun 15 05:30:51 server kernel: ata1.00: cmd 25/00:08:42:23:d2/00:00:2c:00:00/e0 tag 0 cdb 0x0 data 4096 in
Jun 15 05:30:51 server kernel: res 51/40:00:42:23:d2/00:00:2c:00:00/e0 Emask 0x9 (media error)
Jun 15 05:30:51 server kernel: ata1.00: configured for UDMA/133
Jun 15 05:30:52 server kernel: ata1: EH complete
Jun 15 05:31:26 server kernel: ata1.00: configured for UDMA/133
Jun 15 05:31:30 server kernel: sd 0:0:0:0: SCSI error: return code = 0x08000002
Jun 15 05:31:33 server kernel: sda: Current [descriptor]: sense key: Medium Error
Jun 15 05:31:36 server kernel: Add. Sense: Unrecovered read error - auto reallocate failed
Jun 15 05:31:36 server kernel:
Jun 15 05:31:39 server kernel: Descriptor sense data with sense descriptors (in hex):
Jun 15 05:31:46 server kernel: 72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00
Jun 15 05:31:51 server kernel: 2c d2 23 42
Jun 15 05:31:56 server kernel: end_request: I/O error, dev sda, sector 751969090
Jun 15 05:31:57 server kernel: ata1: EH complete
Jun 15 05:31:57 server kernel: SCSI device sda: 976773168 512-byte hdwr sectors (500108 MB)
Jun 15 05:31:58 server kernel: sda: Write Protect is off
Jun 15 05:31:58 server kernel: SCSI device sda: drive cache: write back
Jun 15 05:31:59 server kernel: SCSI device sda: 976773168 512-byte hdwr sectors (500108 MB)
Jun 15 05:32:03 server kernel: sda: Write Protect is off
Jun 15 05:32:04 server kernel: SCSI device sda: drive cache: write back
-------------------
is it safe ? or any hardware error?
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Jul 7, 2009
can i upgrade my kernel?
yum cant find any new update but my kernel version is 2.6.18-128.1.1.el5.028stab062.3PAE
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Jun 13, 2009
I have following error in kernel update with yum:
Downloading Packages:
Running rpm_check_debug
ERROR with rpm_check_debug vs depsolve:
Package kernel conflicts with ecryptfs-utils < 44.
Complete!
So kernel not updated yet.
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Jun 20, 2009
I copied the default config file and renamed it as .config but I get this:
Code:
WARNING: No module dm-mem-cache found for kernel 2.6.27.10-grsec, continuing anyway
WARNING: No module dm-region_hash found for kernel 2.6.27.10-grsec, continuing anyway
WARNING: No module dm-message found for kernel 2.6.27.10-grsec, continuing anyway
WARNING: No module dm-raid45 found for kernel 2.6.27.10-grsec, continuing anyway
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Jul 20, 2009
My current kernel version is "2.6.9-42.0.10.ELsmp #1 SMP Fri Feb 16 17:17:21 EST 2007 i686 athlon i386 GNU/Linux". I want it to be upgraded since it is old. I have been told by our server management company that the latest kernel distributed from yum is kernel.i686 0:2.6.9-78.0.22.E. Can anyone tell me if this version is safe and secure enough? It is a CentOS release 4.7 (Final) server with cPanel installed.
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Aug 1, 2009
i have a dedicated server with Centos 5.2 32bit.
my cpu is 64bit but for some software, datacenter install 32bit for me.
i need more ram and order to datacenter, before my ram was 4 Gig and now my ram is 6 gig . but cpu just use 3 gig of ram.
i install kernel-PAE with "yum install kernel-PAE " command and my ram down to 2.5 Gig. now my server used just 2.5 gig of ram.
i can not reformat server because of i have some vps in this server ( Xen vps )
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Jul 12, 2009
when doing 2.6.26+ or w/e it is, how do you enable conntrack, what options do i need to enable under make menuconfig?
net.netfilter.nf_conntrack_acct = 1
net.netfilter.nf_conntrack_generic_timeout = 120
error: "net.netfilter.nf_conntrack_icmp_timeout" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_close" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_time_wait" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_last_ack" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_close_wait" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_fin_wait" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_established" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_syn_recv" is an unknown key
error: "net.netfilter.nf_conntrack_tcp_timeout_syn_sent" is an unknown key
error: "net.netfilter.nf_conntrack_udp_timeout" is an unknown key
error: "net.netfilter.nf_conntrack_udp_timeout_stream" is an unknown key
net.netfilter.nf_conntrack_max = 262144
and how do i know which hardware/devices that i can remove?
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Jul 24, 2009
I have a FreeBSD server crashing a few times per week sometimes 2 or 3 times in one day, then 3 days fine sometimes each other day...
/var/log/messages shows nothing related to the reboot when looking at the server screen after a crash, it showed kernel panic
any ideas on how to troubleshoot that with the minimum downtime possible? DC already tried swapping memory, but it didn't solve
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May 12, 2008
I am using centos 4.6 on 2.6.9-67smp kernel
I need to update the kernel to 2.6.25.3
is that possible ?
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Dec 24, 2008
I've never actually compiled a kernel before, and wanted to know the basics when it comes to compiling for a standard CPanel/Centos 32bit system.
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Jul 9, 2008
i compiled my kernel and i have problem.. i dont have lilo on my server so i dont know how to change the grub.conf file to boot my new kernel..
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Jun 28, 2008
How Can i translate An Kernel Exploit to secure my server like that
[url]
how can i now what i do to my server if i see any exploit
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Apr 26, 2008
I have always used RPM kernels from the RedHat Network, in this time I need to compile an SMP kernel in a server that is used to serve common webhosting traffic (web, ftp, email, etc) with cPanel.
I have compiled kernels from source in desktops stations, but never in remote servers.. do you have any recommendations to do this at a Dual Xeon 3.2 RHE 5 + cPanel server? Oh.. almost forgot.. I will also compile it with GRsecurity.
Should I use a src kernel from RedHat, or a kernel.org latest kernel?
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May 8, 2008
I installed CentOS 5 on a server with 2 quad core CPU's and 4GB of RAM. After the installation is done and during boot I see a warning that says "Warning only 3GB will be used".
So, just to check, I installed CentOS 4.4 and it sees all 4GB of RAM.
Are there any memory limitations on the distro? or could it be that the desktop kernels made their way into the iso's from upstream?
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