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SubjectRe: Kernel 2.6.21.3 does not work with 8GB of RAM on Intel 965WH motherboards.
Justin Piszcz wrote:
> Short Description of Problem:
> Linux 2.6.21.3 does not run properly with 8GB of ram on the Intel 965WH
> motherboard.
>
> Long Description of Problem:
> When I use 8GB of memory on my x86_64 system, CPU-bound processes are VERY
> slow, up to 36x slower than usual. My temporary fix is force Linux to only
> use 4GB of memory, I am currently using mem=4096M. I ran memtest86 and the
> memory is fine, not a single error. I tried the following to mem= 1024,
> 2048
> 4096 and blank "" to let the kernel use all 8GB of memory. What is wrong
> with the kernel and how come it cannot use 8GB of memory without slowing
> down
> all CPU-related processes to a snail-like pace? There is something
> horribly
> wrong here.
>
> Specifications:
> Intel Motherboard: 965WH
> Linux Kernel: 2.6.21.3
> Distribution: Debian Testing x86_64
> GCC: gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
> Target: x86_64-linux-gnu
>
> Tests:
>
> 1. append line = 1024M
> top - 18:28:26 up 1 min, 4 users, load average: 0.42, 0.17, 0.06
> Tasks: 157 total, 1 running, 156 sleeping, 0 stopped, 0 zombie
> Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si,
> 0.0%st
> Mem: 1027016k total, 964288k used, 62728k free, 1232k buffers
> Swap: 16787768k total, 0k used, 16787768k free, 105168k cached
> ---> STATUS: No problems, box is fine, no lag, etc..
>
> 2. append line = 2048M
> top - 18:34:23 up 2 min, 2 users, load average: 0.14, 0.14, 0.05
> Tasks: 147 total, 1 running, 146 sleeping, 0 stopped, 0 zombie
> Cpu(s): 1.7%us, 1.2%sy, 0.4%ni, 95.2%id, 1.5%wa, 0.0%hi, 0.0%si,
> 0.0%st
> Mem: 2059696k total, 956324k used, 1103372k free, 1232k buffers
> Swap: 16787768k total, 0k used, 16787768k free, 102924k cached
> ---> STATUS: No problems, box is fine, no lag, etc..
>
> 3. append line = 4096M
> top - 18:37:55 up 1 min, 1 user, load average: 0.52, 0.19, 0.07
> Tasks: 143 total, 1 running, 142 sleeping, 0 stopped, 0 zombie
> Cpu(s): 2.9%us, 2.2%sy, 0.7%ni, 91.6%id, 2.6%wa, 0.0%hi, 0.0%si,
> 0.0%st
> Mem: 3339536k total, 949792k used, 2389744k free, 1232k buffers
> Swap: 16787768k total, 0k used, 16787768k free, 99920k cached
>
> $ time ssh p34 uptime
> 19:00:16 up 1 min, 1 user, load average: 0.67, 0.18, 0.06
> real 0m0.159s
> user 0m0.013s
> sys 0m0.003s
> ---> STATUS: No problems, box is fine, no lag, etc..
>
> 4. append line = "" (use all 8GB)
>
> top - 18:52:50 up 9 min, 1 user, load average: 2.88, 2.43, 1.41
> Tasks: 149 total, 3 running, 146 sleeping, 0 stopped, 0 zombie
> Cpu(s): 36.3%us, 2.2%sy, 10.3%ni, 50.8%id, 0.4%wa, 0.0%hi, 0.1%si,
> 0.0%st
> Mem: 8104460k total, 1064416k used, 7040044k free, 3296k buffers
> Swap: 16787768k total, 0k used, 16787768k free, 201852k cached
>
> $ ssh p34
> ssh: connect to host p34 port 22: Connection refused
>
> Machine takes 5-10 minutes to boot, it acts like a 286 computer, about 8
> minutes later:
>
> $ time ssh p34 uptime # 5 SECONDS!! 36x slower when using 8GB of RAM
> 18:51:39 up 8 min, 1 user, load average: 2.74, 2.31, 1.30
>
> real 0m5.757s
> user 0m0.015s
> sys 0m0.004s
>
> The machine is VERY slow and this is on a gigabit network, I/O does not
> seem to be affected but rather, CPU-bound processes.
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 2483 root 25 0 25324 5292 1072 R 96 0.1 4:37.12 mailgraph
> 3604 logcheck 30 10 3408 1120 544 R 91 0.0 0:03.55 grep
>
> These normally take seconds but when I use all 8GB of memory, it runs
> for a very long time.
>
> Conclusion: For now, I will be using mem=4096M until someone can help me
> understand what is happening here. Can anyone offer any insight?
>
> I found it interesting in make menuconfig on x86_64 there is no 4GB/64GB
> options in the kernel that I remember seeing in 32bit.

That's because that option is not applicable in 64-bit mode.

Can you send your full dmesg output from the 8GB bootup?

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

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