From: Jakub Jelinek <jakub@redhat.com>
To: Peter Waechtler <pwaechtler@mac.com>
Cc: Jamie Lokier <jamie@shareable.org>,
Ulrich Drepper <drepper@redhat.com>,
Krzysztof Benedyczak <golbi@mat.uni.torun.pl>,
linux-kernel@vger.kernel.org,
Manfred Spraul <manfred@colorfullife.com>,
Michal Wronski <wrona@mat.uni.torun.pl>
Subject: Re: POSIX message queues
Date: Tue, 7 Oct 2003 04:11:26 -0400 [thread overview]
Message-ID: <20031007041126.C26086@devserv.devel.redhat.com> (raw)
In-Reply-To: <1448383.1065513016965.JavaMail.pwaechtler@mac.com>; from pwaechtler@mac.com on Tue, Oct 07, 2003 at 09:50:16AM +0200
On Tue, Oct 07, 2003 at 09:50:16AM +0200, Peter Waechtler wrote:
>
> On Sunday, October 05, 2003, at 08:32PM, Jakub Jelinek <jakub@redhat.com> wrote:
>
> >> Speaking of librt - I should not have to link in pthreads and the
> >> run-time overhead associated with it (locking stdio etc.) just so I
> >> can use shm_open(). Any chance of fixing this?
> >
> >That overhead is mostly gone in current glibcs (when using NPTL):
> >a) e.g. locking is done unconditionally even when libpthread is not present
> > (it is just lock cmpxchgl, inlined)
>
>
> a "lock cmpxchg" is > 100 cycles (according to a recent Linux Journal article
> from Paul McKenney: 107ns on 700MHz PentiumIII)
Here is exactly what it does on IA-32/i686+:
# define lll_lock(futex) \
(void) ({ int ignore1, ignore2; \
__asm __volatile ("cmpl $0, %%gs:%P6\n\t" \
"je,pt 0f\n\t" \
"lock\n" \
"0:\tcmpxchgl %1, %2\n\t" \
"jnz _L_mutex_lock_%=\n\t" \
".subsection 1\n\t" \
".type _L_mutex_lock_%=,@function\n" \
"_L_mutex_lock_%=:\n\t" \
"leal %2, %%ecx\n\t" \
"call __lll_mutex_lock_wait\n\t" \
"jmp 1f\n\t" \
".size _L_mutex_lock_%=,.-_L_mutex_lock_%=\n" \
".previous\n" \
"1:" \
: "=a" (ignore1), "=c" (ignore2), "=m" (futex) \
: "0" (0), "1" (1), "m" (futex), \
"i" (offsetof (tcbhead_t, multiple_threads)) \
: "memory"); })
> you suggested naming the syscall number symbols NR_mq_open instead of
> NR_sys_mq_open. In the stub I want to overload some syscalls (e.g. mq_open)
> but others not (e.g. mq_timedsend).
>
> How to deal with that?
The syscall is still mq_open, isn't it? So it should be __NR_mq_open.
You simply put the ones where you want to implement them directly in the kernel
into syscalls.list (and add sysdeps/generic/mq_*.c stubs; also, mq_{timed,}{receive,send}
are cancellation points according to POSIX 2003, so they need to be marked as such).
Where you need to do some handling before/after the syscall in userland, you simply write
mq_open.c etc. and use INLINE_SYSCALL (or INTERNAL_SYSCALL) in it.
Jakub
next prev parent reply other threads:[~2003-10-07 8:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-07 7:50 POSIX message queues Peter Waechtler
2003-10-07 8:11 ` Jakub Jelinek [this message]
-- strict thread matches above, loose matches on Subject: below --
2003-10-05 9:13 Krzysztof Benedyczak
2003-10-05 10:11 ` Manfred Spraul
2003-10-06 19:04 ` Krzysztof Benedyczak
2003-10-05 16:35 ` Ulrich Drepper
2003-10-05 18:16 ` Jamie Lokier
2003-10-05 18:32 ` Jakub Jelinek
2003-10-05 19:18 ` Jamie Lokier
2003-10-05 21:52 ` Ulrich Drepper
2002-10-02 10:35 Krzysztof Benedyczak
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