linux-kernel - Re: [PATCH] nvme-pci: 512 byte aligned dma pool segment quirk

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Message-ID: <19327249129.1131b0ddd320896.1106904208694557670@collabora.com>
Date: Wed, 13 Nov 2024 20:08:48 +0000
From: Robert Beckett <bob.beckett@...labora.com>
To: "Keith Busch" <kbusch@...nel.org>
Cc: "Christoph Hellwig" <hch@....de>, "Jens Axboe" <axboe@...nel.dk>,
	"Sagi Grimberg" <sagi@...mberg.me>, "kernel" <kernel@...labora.com>,
	"linux-nvme" <linux-nvme@...ts.infradead.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvme-pci: 512 byte aligned dma pool segment quirk






 ---- On Wed, 13 Nov 2024 18:05:53 +0000  Keith Busch  wrote --- 
 > On Wed, Nov 13, 2024 at 05:31:51AM +0100, Christoph Hellwig wrote:
 > > On Tue, Nov 12, 2024 at 07:50:00PM +0000, Bob Beckett wrote:
 > > > From: Robert Beckett bob.beckett@...labora.com>
 > > > 
 > > > We initially put in a quick fix of limiting the queue depth to 1
 > > > as experimentation showed that it fixed data corruption on 64GB
 > > > steamdecks.
 > > > 
 > > > After further experimentation, it appears that the corruption
 > > > is fixed by aligning the small dma pool segments to 512 bytes.
 > > > Testing via desync image verification shows that it now passes
 > > > thousands of verification loops, where previously
 > > > it never managed above 7.
 > > 
 > > As suggested before, instead of changing the pool size please just
 > > always use the large pool for this device.
 > 
 > Well, he's doing what I suggested. I thought this was better because it
 > puts the decision making in the initialization path instead of the IO
 > path.
 > 
yep, this avoids any extra conditional in the fast path