linux-kernel - Re: [PATCH 1/9] move blk_iopoll to limit and make it generally available

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Date:	Sun, 15 Nov 2015 13:51:59 +0100
From:	Christoph Hellwig <hch@....de>
To:	Sagi Grimberg <sagig@....mellanox.co.il>
Cc:	Christoph Hellwig <hch@....de>, Or Gerlitz <gerlitz.or@...il.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	Bart Van Assche <bart.vanassche@...disk.com>, axboe@...com,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] move blk_iopoll to limit and make it generally
	available

On Sun, Nov 15, 2015 at 10:48:41AM +0200, Sagi Grimberg wrote:
> I have attempted to convert iser to use blk_iopoll in the past, however
> I've seen inconsistent performance and latency skews (comparing to
> tasklets iser is using today). This was manifested in IOPs test cases
> where I ran multiple threads with higher queue-depth and not in
> sanitized pure latency (QD=1) test cases. Unfortunately I didn't have
> the time to pick it up since.
>
> I do have every intention of testing it again with this. If it still
> exist we will need to find the root-cause of it before converting
> drivers to use it.

Thanks.  If you see issue like that with high iops and high loads
the next thing to check are:

 a) increasing the budget (both in the main poll loop and the IB
    code)
 b) try without the single jiffie time limit in the main softirq handler
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