Bug 18272

Summary: 2.6.35.*: horrible (exponential? >linear) slowdown to unusability (ACPI idle?)
Product: Platform Specific/Hardware Reporter: Maciej Rutecki (maciej.rutecki)
Component: x86-64Assignee: platform_x86_64 (platform_x86_64)
Status: CLOSED CODE_FIX    
Severity: normal CC: maciej.rutecki, nix, rjw, tglx
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 2.6.35 Subsystem:
Regression: Yes Bisected commit-id:
Bug Depends on:    
Bug Blocks: 16055    

Description Maciej Rutecki 2010-09-11 19:59:36 UTC 
Subject    : 2.6.35.*: horrible (exponential? >linear) slowdown to unusability (ACPI idle?)
Submitter  : Nix <nix@esperi.org.uk>
Date       : 2010-09-05 0:51
Message-ID : 87zkvx2ese.fsf@spindle.srvr.nix
References : http://marc.info/?l=linux-kernel&m=128364994602942&w=2

This entry is being used for tracking a regression from 2.6.34. Please don't
close it until the problem is fixed in the mainline.

Caused by:

commit 30a564be9d9554c168a654eddc2165869cc0d7bf
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Tue Apr 13 15:31:36 2010 +0200

    x86, hpet: Restrict read back to affected ATI chipsets

    After programming the HPET, we do a readback as a workaround for
    ATI/SBx00 chipsets as a synchronization.  Unfortunately this triggers
    an erratum in newer ICH chipsets (ICH9+) where reading the comparator
    immediately after the write returns the old value.  Furthermore, as
    always, I/O reads are bad for performance.

    Therefore, restrict the readback to the chipsets that need it, or, for
    debugging purposes, when we are running with hpet=verbose.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Venkatesh Pallipadi <venki@google.com>
    LKML-Reference: <20100225185348.GA9674@linux-os.sc.intel.com>
    Signed-off-by: H. Peter Anvin <hpa@zytor.com>

First-Bad-Commit : 30a564be9d9554c168a654eddc2165869cc0d7bf
Comment 1 Rafael J. Wysocki 2010-09-20 20:41:58 UTC 
On Monday, September 20, 2010, Nix wrote:
> On 20 Sep 2010, Rafael J. Wysocki said:
> 
> > This message has been generated automatically as a part of a report
> > of regressions introduced between 2.6.34 and 2.6.35.
> >
> > The following bug entry is on the current list of known regressions
> > introduced between 2.6.34 and 2.6.35.  Please verify if it still should
> > be listed and let the tracking team know (either way).
> 
> Resolved by 54ff7e595d763d894104d421b103a89f7becf47c in master,
> which is landing in 2.6.35.5 imminently.