Message-ID: <3A2FDC3C.C2DA705D@mvista.com>
Date: Thu, 07 Dec 2000 10:51:40 -0800
From: Jun Sun <jsun@mvista.com>
MIME-Version: 1.0
To: kuznet@ms2.inr.ac.ru
CC: linux-kernel@vger.kernel.org
Subject: Re: [Fwd: lost need_resched flag re-introduced?]
In-Reply-To: <200012071721.UAA30863@ms2.inr.ac.ru>
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Sender: linux-kernel-owner@vger.kernel.org

kuznet@ms2.inr.ac.ru wrote:
> 
> Hello!
> 
> > > A while back I reported the lost need_resched flag bug ( it happens if
> > > need_resched is set right before switch_to() is called).  Later on a one-line
> > > fix is added to __schedule_tail().
> > >
> > >         current->need_resched |= prev->need_resched;
> > >
> > > I looked at the latest kernel and found this one is gone.  Is the lost
> > > need_resched problem taken care of in some other way?  Or is it re-introduced?
> 
> It is removed not only because it was wrong (which you have found too),
> but because it was useless even if copied correctly.
> 
> current->need_resched is not changed in interrupt context outside
> runqueue lock except for scheduler timer, where copying results
> in nothing but spurious reschedule.
> 
> Alexey

Alexey,

I think wake_up_process() is called in interrupt routine quite often and it
will set need_resched flag (through reschedule_idle()).  ???

I did several run time tests and confirmed the missing need_resched flag was
happening.  Ether some new code takes care of it.  Or it is still there.

Jun
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