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Date: Wed, 4 Jun 2014 12:35:45 +0200
From: Alexander Gordeev <agordeev@...hat.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-kernel@...r.kernel.org, Ming Lei <tom.leiming@...il.com>
Subject: blk-mq: bitmap tag: performance degradation?
Hi Jens, et al
With new bitmap tags I am observing performance degradation on 'null_blk'
device with 512 queue depth. This is 'fio' config used:
[global]
bs=4k
size=16g
[nullb]
filename=/dev/nullb0
direct=1
rw=randread
numjobs=8
I tried machines with 16 and 48 CPUs and it seems the more
CPUs we have the worse the result. Here is 48 CPUs one:
3.15.0-rc4+
READ: io=131072MB, aggrb=3128.7MB/s, minb=400391KB/s, maxb=407204KB/s,
mint=41201msec, maxt=41902msec
548,549,235,428 cycles:k
3,759,335,303 L1-dcache-load-misses
419,021,008 cache-misses:k
39.659121371 seconds time elapsed
3.15.0-rc1.for-3.16-blk-mq-tagging+
READ: io=131072MB, aggrb=1951.8MB/s, minb=249824KB/s, maxb=255851KB/s,
mint=65574msec, maxt=67156msec
1,063,669,976,651 cycles:k
4,572,746,591 L1-dcache-load-misses
1,127,037,813 cache-misses:k
69.446112553 seconds time elapsed
Thanks!
--
Regards,
Alexander Gordeev
agordeev@...hat.com
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