linux-kernel - Re: [PATCH 0/3]: blk-iopoll, a polled completion API for block devices

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Date:	Tue, 11 Aug 2009 20:49:16 +0200
From:	Bart Van Assche <bart.vanassche@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	Eric.Moore@....com, jeff@...zik.org
Subject: Re: [PATCH 0/3]: blk-iopoll, a polled completion API for block 
	devices

On Tue, Aug 11, 2009 at 8:41 PM, Jens Axboe<jens.axboe@...cle.com> wrote:
> On Tue, Aug 11 2009, Bart Van Assche wrote:
>> On Tue, Aug 11, 2009 at 7:14 PM, Jens Axboe<jens.axboe@...cle.com> wrote:
>> > Did you profile this? Where did it burn all the CPU time on the
>> > initiator side?
>>
>> The test I ran involved a Linux SRP initiator and a Linux SRP target
>> (SCST) using a RAM disk as backstorage. Read throughput is about 1700
>> MB/s for block sizes of 8 MB and above. But with a block size of 4 KB,
>> the read throughput on the initiator drops to 100 MB/s. At this block
>> size there are about 50.000 interrupts per second generated by the
>> InfiniBand HCA in the initiator system. On the same setup the
>> ib_send_bw tool reports a throughput of 1850 MB/s for a block size of
>> 4 KB. This last tool is not interrupt driven but uses polling.
>
> OK, so that looks promising at least. Which hw driver does it use? If I
> look under infiniband/, I see nes, amso, ehca, various ipath and mthca.
> That's where it needs to be hooked up, the srp above mostly looks like
> library helpers and the target hook to the scsi layer.

The above numbers have been obtained on Mellanox ConnectX hardware.
This hardware is controlled by the mlx4_core and mlx4_ib kernel
modules. Source code for these drivers can be found in
drivers/infiniband/hw/mlx4 and drivers/net/mlx4.

Bart.
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