linux-kernel - Re: [PATCH] sched_clock: add data pointer argument to read callback

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

Date:	Sat, 10 Oct 2015 00:48:22 +0100
From:	Måns Rullgård <mans@...sr.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-cris-kernel@...s.com,
	linux-mips@...ux-mips.org, linux-xtensa@...ux-xtensa.org,
	kernel@...inux.com, linux-rpi-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH] sched_clock: add data pointer argument to read callback

Russell King - ARM Linux <linux@....linux.org.uk> writes:

> On Fri, Oct 09, 2015 at 10:57:35PM +0100, Mans Rullgard wrote:
>> This passes a data pointer specified in the sched_clock_register()
>> call to the read callback allowing simpler implementations thereof.
>> 
>> In this patch, existing uses of this interface are simply updated
>> with a null pointer.
>
> This is a bad description.  It tells us what the patch is doing,
> (which we can see by reading the patch) but not _why_.  Please include
> information on why the change is necessary - describe what you are
> trying to achieve.

Currently most of the callbacks use a global variable to store the
address of a counter register.  This has several downsides:

- Loading the address of a global variable can be more expensive than
  keeping a pointer next to the function pointer.

- It makes it impossible to have multiple instances of a driver call
  sched_clock_register() since the caller can't know which clock will
  win in the end.

- Many of the existing callbacks are practically identical and could be
  replaced with a common generic function if it had a pointer argument.

If I've missed something that makes this a stupid idea, please tell.

-- 
Måns Rullgård
mans@...sr.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/