linux-kernel - Re: [PATCH 2/4] set_restore_sigmask TIF

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Message-ID: <alpine.LFD.1.00.0803281942440.14670@woody.linux-foundation.org>
Date:	Fri, 28 Mar 2008 19:52:06 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Roland McGrath <roland@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390@...r.kernel.org, tony.luck@...el.com,
	linux-ia64@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] set_restore_sigmask TIF_SIGPENDING

On Fri, 28 Mar 2008, Roland McGrath wrote:
> 
> It could be a PF_* too, I suppose.  There aren't too many of those
> bits free, but it would have the advantage of being a place for an
> arch that doesn't store any TS_* bits anywhere.

Yeah, I guess PF_ would be a bit more regular. Maybe we should even try to 
avoid the use of TS_ in x86, and turn it into PF_. There are probably bad 
historical reasons for the duplication of capabilities.

> Since acting on the flag is in arch signal code anyway, it makes some
> sense to let the arch define how it gets that to happen.  I'll send
> some follow-on patches that change the conditionals to use #ifdef
> HAVE_SET_RESTORE_SIGMASK.

Let's see if it matters first. No reason to add another arch-specific 
thing if nobody can even measure this thing, and from a quick look it 
seems like every RESTORE_SIGMASK user is basically an error path for a 
system call. Those few extra cycles really won't be noticeable, we almost 
certainly have better things we could use our energy on.

So never mind. I think your series is fine, and my TS_ idea doesn't really 
look like it's worth it (and using PF_ sounds a bit more palatable since 
we could do it with existing infrastructure, but a quick grep shows that 
there's more users of test_thread_flag(TIF_RESTORE_SIGMASK) than I would 
have expected (and the *testing* is equally cheap for atomic and thread- 
synchronous fields, so that's not a performance issue).

			Linus
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