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SubjectRe: [PATCH 0/4] promote zcache from staging
On 08/07/2012 03:23 PM, Seth Jennings wrote:
> On 07/27/2012 01:18 PM, Seth Jennings wrote:
>> Some benchmarking numbers demonstrating the I/O saving that can be had
>> with zcache:
>>
>> https://lkml.org/lkml/2012/3/22/383
>
> There was concern that kernel changes external to zcache since v3.3 may
> have mitigated the benefit of zcache. So I re-ran my kernel building
> benchmark and confirmed that zcache is still providing I/O and runtime
> savings.

There was a request made to test with even greater memory pressure to
demonstrate that, at some unknown point, zcache doesn't have real
problems. So I continued out to 32 threads:

N=4..20 is the same data as before except for the pswpin values.
I found a mistake in the way I computed pswpin that changed those
values slightly. However, this didn't change the overall trend.

I also inverted the %change fields since it is a percent change vs the
normal case.

I/O (in pages)
normal zcache change
N pswpin pswpout majflt I/O sum pswpin pswpout majflt I/O sum %I/O
4 0 2 2116 2118 0 0 2125 2125 0%
8 0 575 2244 2819 0 4 2219 2223 -21%
12 1979 4038 3226 9243 1269 2519 3871 7659 -17%
16 21568 47278 9426 78272 7770 15598 9372 32740 -58%
20 50307 127797 15039 193143 20224 40634 17975 78833 -59%
24 186278 364809 45052 596139 47406 90489 30877 168772 -72%
28 274734 777815 53112 1105661 134981 307346 63480 505807 -54%
32 988530 2002087 168662 3159279 324801 723385 140288 1188474 -62%

Runtime (in seconds)
N normal zcache %change
4 126 127 1%
8 124 124 0%
12 131 133 2%
16 189 156 -17%
20 261 235 -10%
24 513 288 -44%
28 556 434 -22%
32 1463 745 -49%

%CPU utilization (out of 400% on 4 cpus)
N normal zcache %change
4 254 253 0%
8 261 263 1%
12 250 248 -1%
16 173 211 22%
20 124 140 13%
24 64 114 78%
28 59 76 29%
32 23 45 96%

The ~60% I/O savings holds even out to 32 threads, at which point the
non-zcache case has 12GB of I/O and is taking 12x longer to complete.
Additionally, the runtime savings increases significantly beyond 20
threads, even though the absolute runtime is suboptimal due to the
extreme memory pressure.

Seth



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