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From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>
Cc: Richard Weinberger <richard@nod.at>,
	Christoph Hellwig <hch@lst.de>,
	linux-block@vger.kernel.org, linux-um@lists.infradead.org,
	anton.ivanov@cambridgegreys.com, dwalter@google.com
Subject: Re: [PATCH, RFC] ubd: remove use of blk_rq_map_sg
Date: Wed, 17 Oct 2018 08:21:51 +0200	[thread overview]
Message-ID: <20181017062150.GA22028@lst.de> (raw)
In-Reply-To: <da877cdc-7873-30fd-fa33-72cd48419d46@kernel.dk>

On Tue, Oct 16, 2018 at 08:26:31AM -0600, Jens Axboe wrote:
> > Yes. Shall I send a patch with your suggestion or will you?
> 
> Christoph should just fold it in, the bug only exists after his
> change to it.

Sorry, I missed what suggestion we had.  Is that the patch form Jens
earlier?

> 
> > I have one more question, in your first conversion you set queue_depth to 2.
> > How does one know this value?
> > My conversion has 64, which is more or less an educated guess... ;)
> 
> 64 is most likely just fine. Some drivers rely on having 1 in flight and
> it's easier to manage to just let blk-mq take care of that. Outside of that,
> there aren't any magic values. We should probably just use BLKDEV_MAX_RQ
> for ones that don't have a specific hw limit or need.

Is a queue depth > 1 actually safe for ubd?  There are some odd global
variables tracking struct io_thread_req.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>
Cc: Richard Weinberger <richard@nod.at>,
	linux-um@lists.infradead.org, linux-block@vger.kernel.org,
	dwalter@google.com, Christoph Hellwig <hch@lst.de>,
	anton.ivanov@cambridgegreys.com
Subject: Re: [PATCH, RFC] ubd: remove use of blk_rq_map_sg
Date: Wed, 17 Oct 2018 08:21:51 +0200	[thread overview]
Message-ID: <20181017062150.GA22028@lst.de> (raw)
In-Reply-To: <da877cdc-7873-30fd-fa33-72cd48419d46@kernel.dk>

On Tue, Oct 16, 2018 at 08:26:31AM -0600, Jens Axboe wrote:
> > Yes. Shall I send a patch with your suggestion or will you?
> 
> Christoph should just fold it in, the bug only exists after his
> change to it.

Sorry, I missed what suggestion we had.  Is that the patch form Jens
earlier?

> 
> > I have one more question, in your first conversion you set queue_depth to 2.
> > How does one know this value?
> > My conversion has 64, which is more or less an educated guess... ;)
> 
> 64 is most likely just fine. Some drivers rely on having 1 in flight and
> it's easier to manage to just let blk-mq take care of that. Outside of that,
> there aren't any magic values. We should probably just use BLKDEV_MAX_RQ
> for ones that don't have a specific hw limit or need.

Is a queue depth > 1 actually safe for ubd?  There are some odd global
variables tracking struct io_thread_req.

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  reply	other threads:[~2018-10-17  6:21 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-15  6:56 [PATCH, RFC] ubd: remove use of blk_rq_map_sg Christoph Hellwig
2018-10-15  6:56 ` Christoph Hellwig
2018-10-15  8:40 ` Richard Weinberger
2018-10-15  8:40   ` Richard Weinberger
2018-10-15  8:45   ` Christoph Hellwig
2018-10-15  8:45     ` Christoph Hellwig
2018-10-15 19:17     ` Richard Weinberger
2018-10-15 19:17       ` Richard Weinberger
2018-10-15 20:42       ` Richard Weinberger
2018-10-15 20:42         ` Richard Weinberger
2018-10-15 20:55         ` Christoph Hellwig
2018-10-15 20:55           ` Christoph Hellwig
2018-10-15 21:46           ` Richard Weinberger
2018-10-15 21:46             ` Richard Weinberger
2018-10-15 22:04             ` Jens Axboe
2018-10-15 22:04               ` Jens Axboe
2018-10-15 22:44               ` Richard Weinberger
2018-10-15 22:44                 ` Richard Weinberger
2018-10-16  2:19                 ` Jens Axboe
2018-10-16  2:19                   ` Jens Axboe
2018-10-16  8:38                   ` Richard Weinberger
2018-10-16  8:38                     ` Richard Weinberger
2018-10-16 14:26                     ` Jens Axboe
2018-10-16 14:26                       ` Jens Axboe
2018-10-17  6:21                       ` Christoph Hellwig [this message]
2018-10-17  6:21                         ` Christoph Hellwig
2018-10-18 21:04                         ` Richard Weinberger
2018-10-18 21:04                           ` Richard Weinberger
2018-10-15  8:46   ` Anton Ivanov
2018-10-16 22:43 ` Richard Weinberger
2018-10-16 22:43   ` Richard Weinberger
2018-10-17  6:14   ` Christoph Hellwig
2018-10-17  6:14     ` Christoph Hellwig

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