On Tue 18-02-14 17:34:54, Raghavendra K T wrote:

On 02/18/2014 03:19 PM, Jan Kara wrote:

quoted

On Tue 18-02-14 12:55:38, Raghavendra K T wrote:

quoted

Currently max_sane_readahead() returns zero on the cpu having no local memory node
which leads to readahead failure. Fix the readahead failure by returning
minimum of (requested pages, 512). Users running application on a memory-less cpu
which needs readahead such as streaming application see considerable boost in the
performance.

Result:
fadvise experiment with FADV_WILLNEED on a PPC machine having memoryless CPU
with 1GB testfile ( 12 iterations) yielded around 46.66% improvement.

fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile
32GB* 4G RAM  numa machine ( 12 iterations) showed no impact on the normal
NUMA cases w/ patch.

  Can you try one more thing please? Compare startup time of some big
executable (Firefox or LibreOffice come to my mind) for the patched and
normal kernel on a machine which wasn't hit by this NUMA issue. And don't
forget to do "echo 3 >/proc/sys/vm/drop_caches" before each test to flush
the caches. If this doesn't show significant differences, I'm OK with the
patch.

Thanks Honza, I checked with firefox (starting to particular point)..
I do not see any difference. Both the case took around 14sec.

  Good. You can add my:
Acked-by: Jan Kara <jack@suse.cz>

 ( some time it is even faster.. may be because we do not do free
page calculation?. )

  Hardly, that calculation is just a tiny amount of CPU time in the
startup of the application. If there is really a significant difference, it
might be because we don't preload stuff which isn't used in the end.

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR

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