linux-kernel - kernel building regression on 32-rc5 kernel

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Date:	Tue, 3 Nov 2009 22:42:03 +0800
From:	"Shi, Alex" <alex.shi@...el.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: kernel building regression on 32-rc5 kernel 

I found the kernel building will have about 20%~ 30% regressions on our NHM machines. My kernel build do the following things 15 times: 
make mrproper; echo \"3\">/proc/sys/vm/drop_caches; make defconfig; make -j${2timescpunumbers}
Bisect found it is due to the commitment: 
commit a6151c3a5c8e1ff5a28450bc8d6a99a2a0add0a7
Author: Jens Axboe <jens.axboe@...cle.com>
Date:   Wed Oct 7 20:02:57 2009 +0200
 
    cfq-iosched: apply bool value where we return 0/1

It quite makes me confused, but after reverting this patch the performance recovered. I analyzed the vmstat and "perf record" results, But did not find something strange. Just the "perf stat" shows something different.  
 

Perf stat output of Rc5 kernel: 

  850121.335684  task-clock-msecs         #      1.035 CPUs
         867280  context-switches         #      0.001 M/sec
         266319  CPU-migrations           #      0.000 M/sec
       76663435  page-faults              #      0.090 M/sec
  2697372004020  cycles                   #   3172.926 M/sec  (scaled from 100.00%)
  2779762582367  instructions             #      1.031 IPC    (scaled from 100.00%)
    14230675659  cache-references         #     16.740 M/sec  (scaled from 100.00%)
     3048368747  cache-misses             #      3.586 M/sec  (scaled from 100.00%)
 
821.432570507  seconds time elapsed

 Perf stat output of rc5 without the commit kernel:
  900054.808787  task-clock-msecs         #      1.237 CPUs
         845152  context-switches         #      0.001 M/sec
         252689  CPU-migrations           #      0.000 M/sec
       77495232  page-faults              #      0.086 M/sec
  2470286471361  cycles                   #   2744.596 M/sec
  2684134677043  instructions             #      1.087 IPC
    14685367142  cache-references         #     16.316 M/sec
     2869381827  cache-misses             #      3.188 M/sec
 
  727.415980216  seconds time elapsed

BRG
Alex
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