From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
Sagi Grimberg <sagi@grimberg.me>,
"Martin K . Petersen" <martin.petersen@oracle.com>,
linux-block@vger.kernel.org, linux-nvme@lists.infradead.org
Subject: Re: [PATCH 3/3] nvme: don't set io_opt if NOWS is zero
Date: Mon, 1 Jul 2024 17:11:12 +0200 [thread overview]
Message-ID: <20240701151112.GA1677@lst.de> (raw)
In-Reply-To: <ZoK1WRFbr1dK86FK@kbusch-mbp>
On Mon, Jul 01, 2024 at 07:55:37AM -0600, Keith Busch wrote:
> On Mon, Jul 01, 2024 at 07:17:52AM +0200, Christoph Hellwig wrote:
> > NOWS is one of the annoying "0's based values" in NVMe, where 0 means one
> > and we thus can't detect if it isn't set.
>
> We can detect if it is set based on the namespace features flags,
> though.
Except that the flag covers 5 different flags, for 2 different operations.
> > Thus a NOWS value of 0 means
> > that the Namespace Optimal Write Size is a single LBA, which is clearly
> > bogus. Ignore the value in that case and don't propagate an io_opt
> > value to the block layer.
>
> Hm, why is that clearly bogus? Optane SSDs were optimized for
> single-sector writes.
Because even if they optimize for it, the pure overhead of both
the PCIe physical layer, nvme command overhead and software overhead
will never make it more optimal to split a larger I/O down to this
size, which the optimal write size is about.
next prev parent reply other threads:[~2024-07-01 15:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20240701073115epcas5p3e2758375e272cba80281fe0ac37394d0@epcas5p3.samsung.com>
2024-07-01 5:17 ` io_opt fixups Christoph Hellwig
2024-07-01 5:17 ` [PATCH 1/3] block: remove a duplicate io_min check in blk_validate_limits Christoph Hellwig
2024-07-01 6:37 ` Chaitanya Kulkarni
2024-07-01 7:06 ` Sagi Grimberg
2024-07-01 5:17 ` [PATCH 2/3] block: don't reduce max_sectors based on io_opt Christoph Hellwig
2024-07-01 6:42 ` Chaitanya Kulkarni
2024-07-01 7:08 ` Sagi Grimberg
2024-07-01 5:17 ` [PATCH 3/3] nvme: don't set io_opt if NOWS is zero Christoph Hellwig
2024-07-01 7:02 ` Chaitanya Kulkarni
2024-07-01 7:08 ` Sagi Grimberg
2024-07-01 13:55 ` Keith Busch
2024-07-01 15:11 ` Christoph Hellwig [this message]
2024-07-01 7:24 ` io_opt fixups Nitesh Shetty
2024-07-01 10:22 ` Johannes Thumshirn
2024-07-01 12:53 ` Jens Axboe
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