linux-kernel - Re: [PATCH 0/5] ia64 ski emulator patches

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Date:	Tue, 28 Jan 2014 15:46:21 +0100
From:	Mikael Pettersson <mikpelinux@...il.com>
To:	Mikael Pettersson <mikpelinux@...il.com>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] ia64 ski emulator patches

Mikael Pettersson writes:
 > Mikulas Patocka writes:
 >  > 
 >  > 
 >  > On Sat, 25 Jan 2014, Mikael Pettersson wrote:
 >  > 
 >  > > My ski patches are in <http://user.it.uu.se/~mikpe/linux/patches/ia64/ski-1.3.2/>
 >  > > for now.  I'll post the kernel patches to linux-ia64 @ vger in a few minutes.
 >  > > 
 >  > > /Mikael
 >  > 
 >  > Thanks for the patches.
 >  > 
 >  > Isn't this subject to races? - could it lock up if the signal happens just 
 >  > before the pause syscall?
 >  > 
 >  > +    case SSC_HALT_LIGHT:
 >  > +      /* Sleep until SIGIO or SIGALRM is received; this relies on
 >  > +        keyboard/ethernet input being detected via SIGIO, and the
 >  > +        ITC now being emulated via setitimer() and SIGALRM.  */
 >  > +      pause ();
 >  > +      break;
 >  > +
 > 
 > Thanks for the review. You're right, the pause mustn't happen if
 > itc_itimer_fired == 1.  Let me ponder this for a while...

Ok, I've fixed this in two different ways: one patch which uses pselect,
and one patch which uses plain select + the self-pipe trick.  Both work
in limited testing, but the pselect one is much nicer and appears to have
a little less host CPU overhead, so that's the one I'm stress-testing now.

Both patches have been uploaded to the same place as before.

/Mikael
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