On Tue, Aug 19, 2014 at 03:29:25PM +0100, Mel Gorman wrote:
> On Tue, Aug 19, 2014 at 12:32:52PM +0800, Fengguang Wu wrote:
> > Hi Mel,
> >
> > We noticed the below vm-scalability performance/power regressions on
> > commit 3484b2de9499df23c4604a513b36f96326ae81ad ("mm: rearrange zone
> > fields into read-only, page alloc, statistics and page reclaim lines").
> >
> > 24b7e5819ad5cbe 3484b2de9499df23c4604a513 testbox/testcase/testparams
> > --------------- ------------------------- ---------------------------
> > %stddev %change %stddev
> > \ | /
> > 9.95 ± 2% +69.1% 16.83 ± 5%
> > brickland3/vm-scalability/300s-lru-file-mmap-read
> > 2.32 ± 6% +229.4% 7.63 ± 5%
> > brickland3/vm-scalability/300s-lru-file-readonce
> > 12.27 ± 3% +99.4% 24.46 ± 5% TOTAL vm-scalability.stddev
> >
> > 24b7e5819ad5cbe 3484b2de9499df23c4604a513
> > --------------- -------------------------
> > 13882598 ± 0% -35.8% 8915310 ± 1%
> > brickland3/vm-scalability/300s-lru-file-mmap-read
> > 36379953 ± 1% -64.0% 13093373 ± 0%
> > brickland3/vm-scalability/300s-lru-file-readonce
> > 50262551 ± 0% -56.2% 22008683 ± 0% TOTAL vm-scalability.throughput
> >
>
>
> What units are these? It's completely unclear what is good and bad from the
> figures. 300s-lru-file-mmap-read appears multiple times in this report,
> each with different numbers beside them but little clue as to what they
> mean or what I'm meant to be looking for :(
Sorry the output format is a bit obscure: the stats names are after
the "TOTAL" word, such as TOTAL vm-scalability.stddev, TOTAL
vm-scalability.throughput, ...
> This is the same patch that was reported as having a performance gain in
> another set of tests from lkp so am a little confused.
That can happen some times -- we've seen some commits to benefit some
workloads while hurting some others. I'm now running more complete
test set for the commit, hopefully can get some results tomorrow.
> More importantly, as this patch is primary abougt cache misses it should
> be very unlikely that it makes a noticable difference to IO as the
> relative cost of a cache miss is so low. Similarly any difference it
> makes to reclaim activity is likely to be a coincidence or due to test
> variance.
The test case creates tmpfs files and read them fast to exercise the LRU.
So it's VM test and do not involve disk IO.
Thanks,
Fengguang
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