linux-kernel - Re: [PATCH] FRV: do_gettimeofday() should no longer use tickadj

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <9051.1157971604@warthog.cambridge.redhat.com>
Date:	Mon, 11 Sep 2006 11:46:44 +0100
From:	David Howells <dhowells@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Howells <dhowells@...hat.com>,
	john stultz <johnstul@...ibm.com>,
	Adrian Bunk <bunk@...sta.de>, Andrew Morton <akpm@...l.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] FRV: do_gettimeofday() should no longer use tickadj 

Ingo Molnar <mingo@...e.hu> wrote:

> i cannot find Thomas' recent 2.6 one (Thomas, do you have a link to 
> it?), but i did one 5 years ago:
> 
>  http://people.redhat.com/mingo/irq-rewrite-patches/irq-cleanup-2.4.15-B1.bz2
> 
> in general it's a large but otherwise pretty dumb patch.

I wrote my own patch to test this last Friday.  I found that removing all the
regs pointer passing from the interrupt code reduced interrupt entry with a
warm cache by 1 cpu cycle out of 87, and interrupt exit by 19 cycles out of 99.

I can't tell from that exactly how many instructions/memory accesses have been
removed since the FRV permits two instructions to be executed in one cycle
under some circumstances, and two registers to be stored/loaded in one
instruction.

But the main gain in the exit path has to be due to recovery of the clobbered
regs parameter due to a call inside a loop, possibly in handle_IRQ_event().

I'd expect i386 to do better in cycle reduction because it has fewer registers
and so getting one back should gain more.

David
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/