linux-kernel - Re: [tip:sched/core] sched/balancing: Fix cfs_rq-> task_h

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Date:	Tue, 1 Oct 2013 10:22:38 +0800
From:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	pjt@...gle.com, peterz@...radead.org, tglx@...utronix.de,
	lkp@...org, Fengguang Wu <fengguang.wu@...el.com>,
	Huang Ying <ying.huang@...el.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/balancing: Fix cfs_rq-> task_h_load
 calculation

On Mon, Sep 30, 2013 at 12:14:03PM +0400, Vladimir Davydov wrote:
> On 09/29/2013 01:47 PM, Yuanhan Liu wrote:
> >On Fri, Sep 20, 2013 at 06:46:59AM -0700, tip-bot for Vladimir Davydov wrote:
> >>Commit-ID:  7e3115ef5149fc502e3a2e80719dba54a8e7409d
> >>Gitweb:http://git.kernel.org/tip/7e3115ef5149fc502e3a2e80719dba54a8e7409d
> >>Author:     Vladimir Davydov<vdavydov@...allels.com>
> >>AuthorDate: Sat, 14 Sep 2013 19:39:46 +0400
> >>Committer:  Ingo Molnar<mingo@...nel.org>
> >>CommitDate: Fri, 20 Sep 2013 11:59:39 +0200
> >>
> >>sched/balancing: Fix cfs_rq->task_h_load calculation
> >>
> >>Patch a003a2 (sched: Consider runnable load average in move_tasks())
> >>sets all top-level cfs_rqs' h_load to rq->avg.load_avg_contrib, which is
> >>always 0. This mistype leads to all tasks having weight 0 when load
> >>balancing in a cpu-cgroup enabled setup. There obviously should be sum
> >>of weights of all runnable tasks there instead. Fix it.
> >Hi Vladimir,
> >
> >FYI, Here we found a 17% netperf regression by this patch. Here are some
> >changed stats between this commit 7e3115ef5149fc502e3a2e80719dba54a8e7409d
> >and it's parent(3029ede39373c368f402a76896600d85a4f7121b)
> 
> Hello,
> 
> Could you please report the following info:

Hi Vladimir,

This regression was first found at a 2-core 32 CPU Sandybridge server
with 64G memory. However, I can't ssh to it now and we are off work
this week due to holiday. So, sorry, email response may be delayed.

Then I found this regression exists at another atom micro server as
well. And the following machine and testcase specific info are all from it.

And to not make old data confuse you, here I also update the changed
stats and corresponding text plot as well in attachment.
> 
> 1) the test machine cpu topology (i.e. output of /sys/devices/system/cpu/cpu*/{thread_siblings_list,core_siblings_list})

# grep . /sys/devices/system/cpu/cpu*/topology/{thread_siblings_list,core_siblings_list}
/sys/devices/system/cpu/cpu0/topology/thread_siblings_list:0-1
/sys/devices/system/cpu/cpu1/topology/thread_siblings_list:0-1
/sys/devices/system/cpu/cpu2/topology/thread_siblings_list:2-3
/sys/devices/system/cpu/cpu3/topology/thread_siblings_list:2-3
/sys/devices/system/cpu/cpu0/topology/core_siblings_list:0-3
/sys/devices/system/cpu/cpu1/topology/core_siblings_list:0-3
/sys/devices/system/cpu/cpu2/topology/core_siblings_list:0-3
/sys/devices/system/cpu/cpu3/topology/core_siblings_list:0-3

> 2) kernel config you used during the test

Attached.

> 3) the output of /sys/kernel/debug/sched_features (debugfs mounted).

# cat /sys/kernel/debug/sched_features 
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY
WAKEUP_PREEMPTION ARCH_POWER NO_HRTICK NO_DOUBLE_TICK LB_BIAS NONTASK_POWER
TTWU_QUEUE NO_FORCE_SD_OVERLAP RT_RUNTIME_SHARE NO_LB_MIN NO_NUMA NO_NUMA_FORCE 

> 4) netperf server/client options

Here is our testscript we used:
    #!/bin/bash
    # - test
    
    # start netserver
    netserver
    
    sleep 1
    
    for i in $(seq $nr_threads)
    do
            netperf -t $test -c -C -l $runtime &
    done

Where,
  $test is TCP_SENDFILE,
  $nr_threads is 8, two times of nr cpu
  $runtime is 120s

> 5) did you place netserver into a separate cpu cgroup?

Nope.


Thanks.

	--yliu

View attachment "changed-stats" of type "text/plain" (19211 bytes)

View attachment "config-3.12.0-rc1-00038-g7e3115e" of type "text/plain" (80037 bytes)