From: "Nakajima, Jun" <jun.nakajima@intel.com>
To: "Linus Torvalds" <torvalds@osdl.org>,
"Jamie Lokier" <jamie@shareable.org>
Cc: "Nick Piggin" <piggin@cyberone.com.au>,
"bill davidsen" <davidsen@tmr.com>,
<linux-kernel@vger.kernel.org>
Subject: RE: [CFT][RFC] HT scheduler
Date: Tue, 16 Dec 2003 11:03:59 -0800 [thread overview]
Message-ID: <7F740D512C7C1046AB53446D372001736187C2@scsmsx402.sc.intel.com> (raw)
> > Regarding the overhead of the shared runqueue lock:
> >
> > Is the "lock" prefix actually required for locking between x86
> > siblings which share the same L1 cache?
>
> I bet it is. In a big way.
Of course it is.
>
> The lock does two independent things:
> - it tells the core that it can't just crack up the load and store.
> - it also tells other memory ops that they can't re-order around it.
>
> Neither of these have anything to do with the L1 cache.
>
> In short, I'd be very very surprised if you didn't need a "lock"
prefix
> even between hyperthreaded cores. It might be true in some specific
> implementation of HT, but quite frankly I'd doubt it, and I'd be
willing
> to guarantee that Intel would never make that architectural even if it
was
> true today (ie it would then break on future versions).
Correct. If such a code happens to be working today, it would be broken
anytime.
>
> It should be easy enough to test in user space.
>
> [ Time passes ]
>
> Done. Check this program out with and without the "lock ;" prefix.
With
> the "lock" it will run forever on a HT CPU. Without the lock, it will
show
> errors pretty much immediately when the two threads start accessing
"nr"
> concurrently.
>
> Linus
>
> ----
> #include <pthread.h>
> #include <signal.h>
> #include <unistd.h>
> #include <stdio.h>
>
> unsigned long nr;
>
> #define LOCK "lock ;"
>
> void * check_bit(int bit)
> {
> int set, reset;
> do {
> asm(LOCK "btsl %1,%2; sbbl %0,%0": "=r" (set): "r"
(bit), "m"
> (nr):"memory");
> asm(LOCK "btcl %1,%2; sbbl %0,%0": "=r" (reset): "r"
(bit),
> "m" (nr):"memory");
> } while (reset && !set);
> fprintf(stderr, "bit %d: %d %d (%08x)\n", bit, set, reset, nr);
> return NULL;
> }
>
> static void * thread1(void* dummy)
> {
> return check_bit(0);
> }
>
> static void * thread2(void *dummy)
> {
> return check_bit(1);
> }
>
> int main(int argc, char ** argv)
> {
> pthread_t p;
>
> pthread_create(&p, NULL, thread1, NULL);
> sleep(1);
> thread2(NULL);
> return 1;
> }
> -
> To unsubscribe from this list: send the line "unsubscribe
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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
next reply other threads:[~2003-12-16 19:05 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-12-16 19:03 Nakajima, Jun [this message]
-- strict thread matches above, loose matches on Subject: below --
2003-12-17 0:38 [CFT][RFC] HT scheduler Nakajima, Jun
[not found] <200312161127.13691.habanero@us.ibm.com>
2003-12-16 17:37 ` Andrew Theurer
2003-12-17 2:41 ` Nick Piggin
[not found] <20031213022038.300B22C2C1@lists.samba.org.suse.lists.linux.kernel>
[not found] ` <3FDAB517.4000309@cyberone.com.au.suse.lists.linux.kernel>
[not found] ` <brgeo7$huv$1@gatekeeper.tmr.com.suse.lists.linux.kernel>
[not found] ` <3FDBC876.3020603@cyberone.com.au.suse.lists.linux.kernel>
[not found] ` <20031214043245.GC21241@mail.shareable.org.suse.lists.linux.kernel>
[not found] ` <3FDC3023.9030708@cyberone.com.au.suse.lists.linux.kernel>
[not found] ` <1071398761.5233.1.camel@laptop.fenrus.com.suse.lists.linux.kernel>
2003-12-14 16:26 ` Andi Kleen
2003-12-14 16:54 ` Arjan van de Ven
2003-12-08 4:25 [PATCH][RFC] make cpu_sibling_map a cpumask_t Nick Piggin
2003-12-08 15:59 ` Anton Blanchard
2003-12-08 23:08 ` Nick Piggin
2003-12-09 0:14 ` Anton Blanchard
2003-12-11 4:25 ` [CFT][RFC] HT scheduler Nick Piggin
2003-12-11 7:24 ` Nick Piggin
2003-12-11 8:57 ` Nick Piggin
2003-12-11 11:52 ` William Lee Irwin III
2003-12-11 13:09 ` Nick Piggin
2003-12-11 13:23 ` William Lee Irwin III
2003-12-11 13:30 ` Nick Piggin
2003-12-11 13:32 ` William Lee Irwin III
2003-12-11 15:30 ` Nick Piggin
2003-12-11 15:38 ` William Lee Irwin III
2003-12-11 15:51 ` Nick Piggin
2003-12-11 15:56 ` William Lee Irwin III
2003-12-11 16:37 ` Nick Piggin
2003-12-11 16:40 ` William Lee Irwin III
2003-12-12 0:58 ` Rusty Russell
2003-12-11 10:01 ` Rhino
2003-12-11 8:14 ` Nick Piggin
2003-12-11 16:49 ` Rhino
2003-12-11 15:16 ` Nick Piggin
2003-12-11 11:40 ` William Lee Irwin III
2003-12-11 17:05 ` Rhino
2003-12-11 15:17 ` William Lee Irwin III
2003-12-11 16:28 ` Kevin P. Fleming
2003-12-11 16:41 ` Nick Piggin
2003-12-12 2:24 ` Rusty Russell
2003-12-12 7:00 ` Nick Piggin
2003-12-12 7:23 ` Rusty Russell
2003-12-13 6:43 ` Nick Piggin
2003-12-14 1:35 ` bill davidsen
2003-12-14 2:18 ` Nick Piggin
2003-12-14 4:32 ` Jamie Lokier
2003-12-14 9:40 ` Nick Piggin
2003-12-14 10:46 ` Arjan van de Ven
2003-12-16 17:46 ` Bill Davidsen
2003-12-16 18:22 ` Linus Torvalds
2003-12-17 0:24 ` Davide Libenzi
2003-12-17 0:41 ` Linus Torvalds
2003-12-17 0:54 ` Davide Libenzi
2003-12-16 17:34 ` Bill Davidsen
2003-12-15 5:53 ` Rusty Russell
2003-12-15 23:08 ` Nick Piggin
2003-12-19 4:57 ` Nick Piggin
2003-12-19 5:13 ` Nick Piggin
2003-12-20 2:43 ` Rusty Russell
2003-12-21 2:56 ` Nick Piggin
2004-01-03 18:57 ` Bill Davidsen
2003-12-15 20:21 ` Zwane Mwaikambo
2003-12-15 23:20 ` Nick Piggin
2003-12-16 0:11 ` Zwane Mwaikambo
2003-12-12 8:59 ` Nick Piggin
2003-12-12 15:14 ` Martin J. Bligh
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