linux-kernel - Re: [Scst-devel] ISCSI-SCST performance (with also IET and STGT data)

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Date:	Fri, 3 Apr 2009 19:08:41 +0200
From:	Bart Van Assche <bart.vanassche@...il.com>
To:	Vladislav Bolkhovitin <vst@...b.net>
Cc:	scst-devel <scst-devel@...ts.sourceforge.net>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [Scst-devel] ISCSI-SCST performance (with also IET and STGT data)

On Thu, Apr 2, 2009 at 7:16 PM, Vladislav Bolkhovitin <vst@...b.net> wrote:
> Bart Van Assche, on 04/02/2009 12:14 AM wrote:
>> I have repeated some of these performance tests for iSCSI over IPoIB
>> (two DDR PCIe 1.0 ConnectX HCA's connected back to back). The results
>> for the buffered I/O test with a block size of 512K (initiator)
>> against a file of 1GB residing on a tmpfs filesystem on the target are
>> as follows:
>>
>> write-test: iSCSI-SCST 243 MB/s; IET 192 MB/s.
>> read-test: iSCSI-SCST 291 MB/s; IET 223 MB/s.
>>
>> And for a block size of 4 KB:
>>
>> write-test: iSCSI-SCST 43 MB/s; IET 42 MB/s.
>> read-test: iSCSI-SCST 288 MB/s; IET 221 MB/s.
>
> Do you have any thoughts why writes are so bad? It shouldn't be so..

It's not impossible that with the 4 KB write test I hit the limits of
the initiator system (Intel E6750 CPU, 2.66 GHz, two cores). Some
statistics I gathered during the 4 KB write test:
Target: CPU load 0.5, 16500 mlx4-comp-0 interrupts per second, same
number of interrupts processed by each core (8250/s).
Initiator: CPU load 1.0, 32850 mlx4-comp-0 interrupts per second, all
interrupts occurred on the same core.

Bart.
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