linux-kernel - Should drivers like nvme let userspace control their latency via dev_pm

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-next>] [day] [month] [year] [list]

Date:   Fri, 16 Sep 2016 08:26:03 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Cc:     Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        linux-nvme@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        J Freyensee <james_p_freyensee@...ux.intel.com>,
        Christoph Hellwig <hch@....de>
Subject: Should drivers like nvme let userspace control their latency via dev_pm_qos?

I'm adding power management to the nvme driver, and I'm exposing
exactly one knob via sysfs: the maximum permissible latency.  This
isn't a power domain issue, and it has no dependencies -- it's
literally just the maximum latency that the driver may impose on I/O
for power saving purposes.

ISTM userspace should be able to specify its own latency tolerance in
a uniform way, and dev_pm_qos seems like the natural interface for
this, except that I cannot find a single instance in the tree of *any*
driver using it via the notifier mechanism.  I can find two drivers
that do it using dev_pm_qos_expose_latency_tolerance(), and both are
LPSS drivers?

So: should I be exposing .set_latency_tolerance() or should I just use
a custom sysfs attribute?  Or both?