Re: [PATCH 1/1] scsi: target: Fix write perf due to unneeded throttling

From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: Mike Christie <michael.christie@oracle.com>
Cc: martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
	target-devel@vger.kernel.org
Subject: Re: [PATCH 1/1] scsi: target: Fix write perf due to unneeded throttling
Date: Mon, 21 Aug 2023 17:21:44 -0400	[thread overview]
Message-ID: <yq1ttss5byk.fsf@ca-mkp.ca.oracle.com> (raw)
In-Reply-To: <20230817192902.346791-1-michael.christie@oracle.com> (Mike Christie's message of "Thu, 17 Aug 2023 14:29:02 -0500")

Mike,

> The write back throttling (WBT) code checks if REQ_SYNC | REQ_IDLE is
> set to determine if a write is O_DIRECT vs buffered. If the bits are
> not set then it assumes it's a buffered write and will throttle LIO if
> we hit certain metrics. LIO itself is not using the buffer cache and
> is doing direct IO, so this has us set the direct bits so we are not
> throttled.
>
> When the initiator application is doing direct IO this can greatly
> improve performance. It depends on the backend device but we have seen
> where the WBT code is throttling writes to only 20K IOPs with 4K IOs
> when the device can support 100K+.

Applied to 6.6/scsi-staging, thanks!

-- 
Martin K. Petersen	Oracle Linux Engineering