linux-kernel - Re: scheduler / perf stat question about CPU-migrations

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Message-ID: <20110617024425.GE29725@thunk.org>
Date:	Thu, 16 Jun 2011 22:44:25 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Pádraig Brady <P@...igBrady.com>,
	linux-kernel@...r.kernel.org
Subject: Re: scheduler / perf stat question about CPU-migrations

On Thu, Jun 16, 2011 at 05:18:39PM +0200, Frederic Weisbecker wrote:
> The only solution is too set perf affinity itself:
> 
> 	schedtool -a 1 -e perf stat -- e2fsck -ft /dev/funarg/kbuild

Nope, that doesn't solve the problem:

# schedtool -a 1 -e perf stat -- e2fsck -ft /dev/funarg/kbuild
e2fsck 1.41.14 (22-Dec-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/funarg/kbuild: 223466/1638400 files (0.3% non-contiguous), 4915668/6553600 blocks
Memory used: 2600k/0k (1069k/1532k), time:  6.72/ 1.18/ 0.36
I/O read: 137MB, write: 1MB, rate: 20.38MB/s

 Performance counter stats for 'e2fsck -ft /dev/funarg/kbuild':

       1523.616797 task-clock                #    0.224 CPUs utilized          
              7227 context-switches          #    0.005 M/sec                  
               253 CPU-migrations            #    0.000 M/sec                  
              1936 page-faults               #    0.001 M/sec                  
        4176409631 cycles                    #    2.741 GHz                    
     <not counted> stalled-cycles-frontend 
     <not counted> stalled-cycles-backend  
        4828485353 instructions              #    1.16  insns per cycle        
         877742160 branches                  #  576.091 M/sec                  
           8017490 branch-misses             #    0.91% of all branches        

       6.798746204 seconds time elapsed

Note the 253 CPU migration....

							- Ted
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