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SubjectRe: zcache preliminary benchmark results
On 03/21/2012 06:30 PM, Dan Magenheimer wrote:
> Last November, in an LKML thread I would rather forget*, James
> Bottomley and others asked for some benchmarking to be done for
> zcache (among other things). For various reasons, that benchmarking
> is just now getting underway and more will be done, but it might be
> useful to publish some interesting preliminary results now.

I'd also like to post some zcache performance numbers that suggest
that zcache makes an even more impressive change to the amount
of total I/O when the system is under light to moderate memory
pressure.

Test machine:
Gentoo w/ kernel v3.3 + frontswap (cleancache disabled)
Quad-core i5-2500 @ 3.3GHz
1GB DDR3 1600MHz (limited with mem=1024m on boot)
Filesystem and swap on 2x80G RAID0
majflt are major page faults reported by "time"
pswpin/out is the delta of pswpin/out from /proc/vmstat before and after
the make -jN

Each run started with with swapoff/on and
echo 3 > /proc/sys/vm/drop_caches
I/O
normal zcache change
N pswpin pswpout majflt I/O sum pswpin pswpout majflt I/O sum %I/O
8 0 133 1781 1914 0 0 1835 1835 4%
12 10 1140 1871 3021 0 5 1886 1891 37%
16 675 1978 2330 4983 21 63 3771 3855 23%
20 3420 6197 3421 13038 265 786 5218 6269 52%
24 28358 51884 8865 89107 3944 6227 36048 46219 48%
28 44132 62182 11931 118245 6094 11362 74323 91779 22%
32 94163 125086 22526 241775 22534 32803 179164 234501 3%

Runtime
N normal zcache %change
8 284 280 1%
12 283 281 1%
16 281 280 0%
20 289 310 -7%
24 322 311 3%
28 347 325 6%
32 437 378 14%

%CPU utilization (out of 400% on 4 cpus)
N normal zcache %change
8 245 245 0%
12 249 251 -1%
16 252 252 0%
20 247 255 -3%
24 221 230 -4%
28 204 219 -7%
32 162 187 -15%

Some of my runtime curve N vs %change doesn't match up with
Dan's probably due to differing swap device speeds and I think
my .config had less to build so the runtime magnitudes are less.

Runtime %change will be effected by the swap device speed. But
the I/O reductions are less related to swap device speed and, IMHO,
really show the value of zcache.

Environments with shared storage could particularly like this.
You could enable swap on your machines and frontswap+zcache
would give you an early warning system for memory pressure.
If frontswap starts picking up pages, the admin can get a
warning and zcache will mitigate the swap I/O impacting the
SAN while something is done to relieve the memory pressure.

--
Seth



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