linux-kernel - Question about bcache buckets utilization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Tue, 9 Sep 2014 08:07:35 +0000
From:	"Lulina (A)" <lina.lulina@...wei.com>
To:	"kmo@...erainc.com" <kmo@...erainc.com>
CC:	Guohongzhen <guohongzhen@...wei.com>,
	"linux-bcache@...r.kernel.org" <linux-bcache@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Question about bcache buckets utilization

Hi! Kent Overstreet, I tested bcache branch for jens:
http://evilpiepirate.org/git/linux-bcache.git/log/?h=for-jens

I have a question about buckets utilization, can you help me to resolve it?

This is the test fio cmd:
fio -name iops -rw=randwrite -iodepth=32 -numjobs=1 -filename=/dev/bcache0 -ioengine libaio -direct=1 -bs=4k -size=500M -runtime=600 -time_based -random_distribution=zipf:1.2

My cache device is 1G size, and Hdd device is 5G size. The bucket size is default 512k.
When the test is run, cache is over CUTOFF_WRITEBACK_SYNC after 3 or 4 seconds. The test result is as follows: 

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await  svctm  %util
bcache0           0.00     0.00    0.00 62081.00     0.00   242.50     8.00     0.00    0.01   0.00   0.00
bcache0           0.00     0.00    0.00 72407.00     0.00   282.84     8.00     0.00    0.01   0.00   0.00
bcache0           0.00     0.00    0.00 62990.00     0.00   246.05     8.00     0.00    0.08   0.00   0.00
bcache0           0.00     0.00    0.00  511.00     0.00     2.00     8.00     0.00   62.53   0.00   0.00
bcache0           0.00     0.00    0.00  601.00     0.00     2.35     8.00     0.00   52.73   0.00   0.00

After cache is over CUTOFF_WRITEBACK_SYNC, all writes come down to the hdd, then I got a pool performance.

As the random rang is set to 500M, It will all overlapped in the cache device. 
Why the overlapped buckets can't be reused? Is there any other conditions need to meet?

Thanks,
Lina Lu
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/