Bug 16523 - Kernel detects only 2 processors on Dual Xeon 5520HT on S5500BC mainboard with ACPI disabled
Summary: Kernel detects only 2 processors on Dual Xeon 5520HT on S5500BC mainboard wit...
Status: CLOSED INVALID
Alias: None
Product: ACPI
Classification: Unclassified
Component: Config-Processors (show other bugs)
Hardware: All Linux
: P1 blocking
Assignee: ykzhao
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2010-08-05 16:53 UTC by Oleg Gawriloff
Modified: 2010-09-29 01:46 UTC (History)
3 users (show)

See Also:
Kernel Version: 2.6.31.xx, 2.6.32.xx, 2.6.33.xx
Subsystem:
Regression: No
Bisected commit-id:


Attachments
acpidump (86.07 KB, application/octet-stream)
2010-08-09 08:33 UTC, Oleg Gawriloff
Details

Description Oleg Gawriloff 2010-08-05 16:53:00 UTC
We have server based on Intel S5500 chipset (platform SR1630BC) with dual E5520
(Quad Core with hyper-threading) installed. With 2.6.31.x,2.6.32.x and 2.6.33.xx system number of CPU is 2 instead of 16 (4 logical cores each with 2 threads).

See: http://bugs.gentoo.org/show_bug.cgi?id=308813
Comment 1 ykzhao 2010-08-09 08:23:11 UTC
Hi, Oleg
    From the http://bugs.gentoo.org/show_bug.cgi?id=308813 it seems that the cpu is detected with ACPI. But it fails in cpu detection with ACPI disabled. Right?
    Will you please attach the output of acpidump on this box? The latest acpidump tool(pmtools-2007116) can be downloaded from: http://www.lesswatts.org/projects/acpi/utilities.php

Thanks.
Comment 2 Oleg Gawriloff 2010-08-09 08:33:27 UTC
Created attachment 27385 [details]
acpidump

Yes, you absolutely right. Here's acpidump.
Comment 3 ykzhao 2010-08-23 03:14:54 UTC
Hi, Oleg
    Sorry for the late response.
    From the acpidump in comment #2 it seems that the ACPI table defines the CPU apic info. In such case the number of CPUs can be detected correctly with ACPI enabled.  If the ACPI is disabled, it will use the info parsed from MPS table. Unfortunately the MPS table reports the incorrect CPU info. (Now the MPS table is obsolete).
    Please try the boot option of "acpi=ht" on the 2.6.32/33.x kernel. When the boot option of "acpi=ht" is added, the system will be booted with ACPI disabled. But it will use the info parsed from ACPI table.

BTW:
    Why do you need to boot the system with ACPI disabled? 

Thanks.
Comment 4 ykzhao 2010-08-31 00:45:35 UTC
Now the ACPI is the default configuration for X86_32/64 platform. The issue is also related with the bogus MPS table when ACPI is disabled. And as this issue only happens with ACPI disabled, this bug will be rejected. 

BTW: the issue can be workaround by adding the boot option of "acpi=ht", which will boot the system with ACPI disabled. But the CPU info parse from ACPI table will be used.

Thanks.
Comment 5 Len Brown 2010-09-29 01:46:23 UTC
Please re-open if you have a problem with the system in ACPI mode.

If you want to run in MPS mode, use a computer with a BIOS
that properly supports MPS.  Note, however, that even if
implemented properly, MPS does not enumerate HT siblings.

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