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From: Jamie Lokier <jamie@shareable.org>
To: Willy Tarreau <willy@w.ods.org>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: TSCs are a no-no on i386
Date: Thu, 31 Jul 2003 16:07:58 +0100	[thread overview]
Message-ID: <20030731150758.GE6410@mail.jlokier.co.uk> (raw)
In-Reply-To: <20030731071719.GA26249@alpha.home.local>

Willy Tarreau wrote:
> The other problem lies with the lock :
> When a 486 executes "LOCK ; CMPXCHG", it locks the bus during the whole cmpxchg
> instruction. If a 386 executes the same code, it will get an exception which
> will be caught by the emulator. I don't see how we can do such an atomic
> operation while holding a lock. At best, we would think about a global memory
> based shared lock during the operation (eg: int bus_lock;), but it's not
> implemented at the moment, and will only be compatible with processors sharing
> the same code. Add-on processors, such as co-processors, transputer cards, or
> DSPs, will know nothing about such a lock emulation. And it would result in
> even poorer performance of course !

Of course this is not a problem when "lock;cmpxchg" is used only for thread
synchronisation on uniprocessor 386s...  The lock prefix is irrelevant then.

Perhaps the emulation should refuse to pretend to work on an SMP 386 :)

-- Jamie

  parent reply	other threads:[~2003-07-31 15:08 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-30 13:56 TSCs are a no-no on i386 Jan-Benedict Glaw
2003-07-30 14:18 ` Maciej W. Rozycki
2003-07-30 14:44   ` Jan-Benedict Glaw
2003-07-30 16:58 ` Matthew Garrett
2003-07-30 17:19   ` Alan Cox
2003-07-30 18:10 ` Adrian Bunk
2003-07-30 18:30   ` Mike Fedyk
2003-07-30 18:45     ` Adrian Bunk
2003-07-30 20:01       ` Alan Cox
2003-07-30 20:33         ` Jan-Benedict Glaw
2003-07-30 22:19           ` J.A. Magallon
2003-07-31  6:11             ` Jan-Benedict Glaw
2003-07-30 23:05           ` Alan Cox
2003-07-31 11:11             ` Richard B. Johnson
2003-07-31 11:26               ` Emulating i486+ insn on i386 (was: TSCs are a no-no on i386) Jan-Benedict Glaw
2003-07-31 11:41             ` TSCs are a no-no on i386 Jan-Benedict Glaw
2003-07-31  0:22           ` Adrian Bunk
2003-07-31  6:22             ` Jan-Benedict Glaw
2003-07-31  7:17               ` Willy Tarreau
2003-07-31 11:38                 ` Emulating i486 on i386 (was: TSCs are a no-no on i386) Jan-Benedict Glaw
2003-07-31 11:51                   ` Alan Cox
2003-07-31 12:14                     ` Jan-Benedict Glaw
2003-07-31 13:01                       ` Jan-Benedict Glaw
2003-07-31 15:09                         ` Martin Schlemmer
2003-07-31 15:33                           ` Jan-Benedict Glaw
2003-08-01  5:37                             ` Martin Schlemmer
2003-07-31 15:12                     ` Jamie Lokier
2003-07-31 15:32                       ` Jan-Benedict Glaw
2003-07-31 15:07                 ` Jamie Lokier [this message]
2003-07-31 15:23                   ` TSCs are a no-no on i386 Willy Tarreau
2003-07-31 15:50                   ` Richard B. Johnson
2003-07-31 16:24                     ` Jan-Benedict Glaw
2003-08-06 11:08         ` Pavel Machek
2003-08-06 14:33           ` Maciej W. Rozycki
2003-07-30 20:28       ` Jan-Benedict Glaw
2003-07-30 21:50         ` Petr Vandrovec
2003-07-30 23:10           ` Alan Cox
2003-07-31 15:10             ` Jamie Lokier
2003-07-31 16:01               ` Alan Cox
2003-07-31 18:37                 ` Jamie Lokier
2003-07-31 19:10                   ` Alan Cox
2003-07-31  6:29           ` Jan-Benedict Glaw
2003-07-30 20:27   ` Jan-Benedict Glaw
2003-08-06 16:41 James Bottomley
2003-08-06 16:45 James Bottomley

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