linux-kernel - Re: [PATCH 3/3] apple-nvme: defer cache flushes by a specified amount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <Z64ZTixWKoYdF8KN@blossom>
Date: Thu, 13 Feb 2025 11:09:50 -0500
From: Alyssa Rosenzweig <alyssa@...enzweig.io>
To: Christoph Hellwig <hch@....de>
Cc: Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>,
	Philipp Zabel <p.zabel@...gutronix.de>, asahi@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] apple-nvme: defer cache flushes by a specified amount

> > Cache flushes on the M1 nvme are really slow, taking 17-18 msec to
> > complete. This can slow down workloads considerably, pure random writes
> > end up being bound by the flush latency and hence run at 55-60 IOPS.
> > 
> > Add a deferred flush work around to provide better performance, at a
> > minimal risk. By default, flushes are delayed at most 1 second, but this
> > is configurable.
> > 
> > With this work-around, a pure random write workload runs at ~12K IOPS
> > rather than 56 IOPS.
> 
> Just as last time this really is not a driver feature.  Cache flushes
> are slow on consumer hardware, it's just apple is worse than usual.
> Breaking file system transactional guarantee by ignoring data integrity
> command in the driver is a no-go.
> 
> If we want to allow an opt-in policy for those whole feel adventurous,
> it belongs into the core flush state machine.  Fortunately the patch
> author seems qualified to touch that :)

Fair enough. I didn't realize this patch was previously discussed, my
apologies. I'll drop this change in v2, and hopefully somebody is
inspired later to do that 'adventure'.