Re: hackbench regression since 2.6.25-rc

[Zhang, Yanmin]

On Thu, 2008-03-13 at 01:48 -0700, Andrew Morton wrote:
> On Thu, 13 Mar 2008 15:46:57 +0800 "Zhang, Yanmin" <yanmin_zhang@xxxxxxxxxxxxxxx> wrote:
> 
> > Comparing with 2.6.24, on my 16-core tigerton, hackbench process mode has about
> > 40% regression with 2.6.25-rc1, and more than 20% regression with kernel
> > 2.6.25-rc4, because rc4 includes the reverting patch of scheduler load balance.
> > 
> > Command to start it.
> > #hackbench 100 process 2000
> > I ran it for 3 times and sum the values.
> > 
> > I tried to investiagte it by bisect.
> > Kernel up to tag 0f4dafc0563c6c49e17fe14b3f5f356e4c4b8806 has the 20% regression.
> > Kernel up to tag 6e90aa972dda8ef86155eefcdbdc8d34165b9f39 hasn't regression.
> > 
> > Any bisect between above 2 tags cause kernel hang. I tried to checkout to a point between
> > these 2 tags for many times manually and kernel always paniced.
> > 
> > All patches between the 2 tags are on kobject restructure. I guess such restructure
> > creates more cache miss on the 16-core tigerton.
> > 
> 
> That's pretty surprising - hackbench spends most of its time in userspace
> and zeroing out anonymous pages.
No. vmstat showed hackbench spends almost 100% in sys.

>   It shouldn't be fiddling with kobjects
> much at all.
> 
> Some kernel profiling might be needed here..
Thanks for your kind reminder. I don't know why I forgot it.

2.6.24 oprofile data:
CPU: Core 2, speed 1602 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
samples  %        image name               app name                 symbol name
40200494 43.3899  linux-2.6.24             linux-2.6.24             __slab_alloc
35338431 38.1421  linux-2.6.24             linux-2.6.24             add_partial_tail
2993156   3.2306  linux-2.6.24             linux-2.6.24             __slab_free
1365806   1.4742  linux-2.6.24             linux-2.6.24             sock_alloc_send_skb
1253820   1.3533  linux-2.6.24             linux-2.6.24             copy_user_generic_string
1141442   1.2320  linux-2.6.24             linux-2.6.24             unix_stream_recvmsg
846836    0.9140  linux-2.6.24             linux-2.6.24             unix_stream_sendmsg
777561    0.8393  linux-2.6.24             linux-2.6.24             kmem_cache_alloc
587127    0.6337  linux-2.6.24             linux-2.6.24             sock_def_readable




2.6.25-rc4 oprofile data:
CPU: Core 2, speed 1602 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
samples  %        image name               app name                 symbol name
46746994 43.3801  linux-2.6.25-rc4         linux-2.6.25-rc4         __slab_alloc
45986635 42.6745  linux-2.6.25-rc4         linux-2.6.25-rc4         add_partial
2577578   2.3919  linux-2.6.25-rc4         linux-2.6.25-rc4         __slab_free
1301644   1.2079  linux-2.6.25-rc4         linux-2.6.25-rc4         sock_alloc_send_skb
1185888   1.1005  linux-2.6.25-rc4         linux-2.6.25-rc4         copy_user_generic_string
969847    0.9000  linux-2.6.25-rc4         linux-2.6.25-rc4         unix_stream_recvmsg
806665    0.7486  linux-2.6.25-rc4         linux-2.6.25-rc4         kmem_cache_alloc
731059    0.6784  linux-2.6.25-rc4         linux-2.6.25-rc4         unix_stream_sendmsg


-yanmin


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