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Message-ID: <4EAE9D3A.7000108@atlas.cz> Date: Mon, 31 Oct 2011 14:06:02 +0100 From: Clarinet <clarinet@...as.cz> To: Ben Hutchings <ben@...adent.org.uk> CC: 647095@...s.debian.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: CPU hyperthreading turned on after soft power-cycle On 10/30/2011 4:25 PM, Ben Hutchings wrote: > On Sun, 2011-10-30 at 07:05 -0400, Jiri Polach wrote: >> Package: linux-2.6 >> Version: 2.6.39-3~bpo60+1 >> Severity: normal >> >> >> When the computer is turned off using "shutdown -h" or "halt" command, >> the hypertherading BIOS setting is changed - even if hypertherading is >> disabled in BIOS, the kernel detects twice as many "processors" on >> next boot as if hyperthreading was enabled. Please see details below. >> >> I have observed the problem on several Supermicro platforms with >> various Intel Xeon processors. The particular case I report was >> observed on Supermicro X8DTT-F mainboard with two Intel Xeon E5645 >> processors (6core). The problem can be reproduced the following way: > > By my understanding of how hyperthreading is controlled, this has to be > a BIOS bug, as you seem to have suspected. But if the BIOS behaviour is > kernel version-dependent, then presumably there is something the kernel > can do to work around it. Yes, there are reasons that support my suspicion that BIOS is not doing its work properly. But I cannot prove it until it is clear what has been changed in the kernel. >> 1. Turn on the computer, go to BIOS setup and turn "Simultaneous >> multithreading" to "Disabled". Boot Debian. >> >> 2. Check with "cat /proc/cpuinfo" that the system reports 12 CPUs (2 x >> six-core processor). >> >> 3. (optionally) Reboot the system (shutdown -r) and check that there >> are still 12 CPUs detected and reported. >> >> 4. Halt the system using "shutdown -h" or "halt", turn it on again, >> and boot Debian. > > I assume from this that shutdown -h is configured to turn the system > off. I do not know. I have been using mostly "halt" to shutdown the system and turn the server off and I tried "shutdown -h" only several times to see if there is any difference. Both commands have turned the computer off, but I did not do any special "shutdown -h" configuration. >> 5. Check the number of CPUs reported - it will show you that there are >> 24 CPUs as if hyperthreading was enabled. >> >> 6. Reboot and go to BIOS setup - it still shows that "Simultaneous >> multithreading" is set to "Disabled". Do not change anythig, just >> select "Save and Exit". Boot Debian and check the number of CPUs - it >> now shows 12 CPUs again. >> >> I have tested several kernel versions and it seems that this behavior >> appeared for the first time somewhere between 2.6.35.7 and 2.6.38.6 >> versions (ok = does not show the decribed behavior, not ok = does >> show): >> >> * linux-image-2.6.32-5-amd64 official Debian - ok >> * linux-image-2.6.39-bpo.2-amd64 official Debian from backports - not >> ok >> >> * linux 2.6.35.7 - custom compiled from source - ok >> * linux 2.6.38.6 - custom compiled from source - not ok >> * linux 2.6.39.4 - custom compiled from source - not ok >> * linux 3.0.4 - custom compiled from source - not ok > > That might be too large a range for developers to consider. Can you > test some versions between 2.6.35.7 and 2.6.38.6 (bisection)? OK, after another day of testing it seems that the problem appears in 2.6.38.1, because * linux 2.6.37.6 - custom compiled from source - ok * linux 2.6.38.1 - custom compiled from source - not ok Best regards, Jiri Polach > Ben. > >> I have exchnged many e-mails with Supermicro distributor who >> apparently is in direct contact with Supermicro technicians. They more >> or less deny any responsibility for this problem and repeatedly point >> to the fact that some (older) kernels do not exhibit this behavior so >> it must be a kernel problem. Their representative writes: >> >> "I discussed this with supermicro and they informed me that the Kernel >> itself is causing the issue, that it may be sending the hyperthreading >> command code to the BIOS." >> >> Although I do not completely agree with their arguments, my knowledge >> is not deep enough to recognize where exactly the core of the problem >> is so I report this as a bug in a hope that someone will know what >> happens when a kernel turns a computer off and what has changed in >> kernel somewhere between the versions I mention above. I have asked >> Supermicro distributor for more information on what they think happens >> there and what exactly they mean by "hyperhreading command code" and I >> am waiting for their response. >> >> -- Package-specific info: >> ** Version: >> Linux version 2.6.39-bpo.2-amd64 (Debian 2.6.39-3~bpo60+1) (norbert@...tkowski.de) (gcc version 4.4.5 (Debian 4.4.5-8) ) #1 SMP Tue Jul 26 10:35:23 UTC 2011 > [...] >> ** Model information >> sys_vendor: Supermicro >> product_name: X8DTT >> product_version: 1234567890 >> chassis_vendor: Supermicro >> chassis_version: 1234567890 >> bios_vendor: American Megatrends Inc. >> bios_version: 080016 >> board_vendor: Supermicro >> board_name: X8DTT >> board_version: 2.0 > [...] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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