From: Willy Tarreau <w@1wt.eu>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH] x86-32: A better system call mechanism
Date: Sun, 1 Apr 2012 08:50:19 +0200 [thread overview]
Message-ID: <20120401065019.GA27590@1wt.eu> (raw)
In-Reply-To: <201204010000.quickdontsayit@terminus.zytor.com>
Hi Peter,
On Sun, Apr 01, 2012 at 12:00:00AM +0000, H. Peter Anvin wrote:
> On x86-32, we currently use int $0x80 as the primary system call
> mechanism. Although there are some recent variants available on
> certain hardware (sysenter, syscall) via the vdso, the primary system
> call vector is still way up the interrupt vector table, which is
> inefficient.
>
> This patch adds a very small amount of code which permits the very
> first vector to be used for system call. That vector is #DE, divide
> error, generally known as division by zero.
Looks like a clever trick, but beyond the beauty, what does it really
save ? Code size is the same as aam 0 / div edx are both 2-byte long,
just like int 0x80. Is the call less expensive ? And if so, how does
it compare to vdso ?
Thanks,
Willy
next prev parent reply other threads:[~2012-04-01 6:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-01 0:00 [PATCH] x86-32: A better system call mechanism H. Peter Anvin
2012-04-01 6:50 ` Willy Tarreau [this message]
2012-04-01 6:52 ` Willy Tarreau
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