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.
Gentoo w/ kernel v3.5 (frontswap only, cleancache disabled)
Quad-core i5-2500 @ 3.3GHz
512MB DDR3 1600MHz (limited with mem=512m on boot)
Filesystem and swap on 80GB HDD (about 58MB/s with hdparm -t)
majflt are major page faults reported by the time command
pswpin/out is the delta of pswpin/out from /proc/vmstat before and after
the make -jN
Mind the 512MB RAM vs 1GB in my previous results. This just reduces
the number of threads required to create memory pressure and removes some
of the context switching noise from the results.
I'm also using a single HDD instead of the RAID0 in my previous results.
Each run started with with:
swapoff -a
swapon -a
sync
echo 3 > /proc/sys/vm/drop_caches
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 4 4 2219 2227 21%
12 2543 4038 3226 9807 1748 2519 3871 8138 17%
16 23926 47278 9426 80630 8252 15598 9372 33222 59%
20 50307 127797 15039 193143 20224 40634 17975 78833 59%
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%
%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%
There is a sweet spot at 16 threads, where zcache is improving runtime by
17% and reducing I/O by 59% (185MB) using 22% more CPU.
Seth
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