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Message-ID: <29495f1d050621115636bc6f77@mail.gmail.com>
Date: Tue, 21 Jun 2005 11:56:30 -0700
From: Nish Aravamudan <nish.aravamudan@gmail.com>
Reply-To: Nish Aravamudan <nish.aravamudan@gmail.com>
To: Lee Revell <rlrevell@joe-job.com>
Subject: Re: -mm -> 2.6.13 merge status
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
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On 6/21/05, Lee Revell <rlrevell@joe-job.com> wrote:
> On Mon, 2005-06-20 at 23:54 -0700, Andrew Morton wrote:
> > CONFIG_HZ for x86 and ia64: changes default HZ to 250, make HZ
> > Kconfigurable.
> >
> >     Will merge (will switch default to 1000 Hz later if that seems
> > necessary)
> 
> Are you serious?  You're changing the *default* HZ in a stable kernel
> series?!?
> 
> This is a big regression, it degrades the resolution of system calls.

Not that my opinion should sway anybody else, but I really would
prefer more of the in-kernel sleep callers were converted to use
human-time units (and thus were verified to be correct) so that
switching HZ will result in the *same* latencies. How much of moving
to lower HZ values is due to the fact that everything is request 10ms
for 1 jiffy of sleep instead of 1 ms? It's hard to tell if the gain is
there or from the lower frequency of interrupts.

I've sent out a lot of patches in this direction (using msleep() and
msleep_interruptible() and my soft-timer rework on top of John
Stultz's timeofday rework converts the entire soft-timer subsystem to
use human-time instead of jiffies as it's unit of expiration), but
there is still *a lot* of work left to do :( I will keep sending
patches, but am being pulled in other directions currently.

Just my $.02.

Thanks,
Nish