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Re: Hitachi djprobe mechanism

From: Andi Kleen <ak at suse dot de>
To: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
Cc: Karim Yaghmour <karim at opersys dot com>,Masami Hiramatsu <masami dot hiramatsu at gmail dot com>,Masami Hiramatsu <hiramatu at sdl dot hitachi dot co dot jp>,Roland McGrath <roland at redhat dot com>,Richard J Moore <richardj_moore at uk dot ibm dot com>,systemtap at sources dot redhat dot com, sugita at sdl dot hitachi dot co dot jp,Satoshi Oshima <soshima at redhat dot com>, michel dot dagenais at polymtl dot ca
Date: 29 Jul 2005 09:54:51 +0200
Subject: Re: Hitachi djprobe mechanism
References: <44BDAFB888F59F408FAE3CC35AB4704101E506F6@orsmsx409><42E83895.6070602@opersys.com> <42E83CEC.8040702@opersys.com><f86b20530507280922819d927@mail.gmail.com><42E90600.3040709@opersys.com> <20050728173515.GB18093@Krystal><20050728110717.A30199@unix-os.sc.intel.com><20050728183234.GC18093@Krystal><20050728133456.A32210@unix-os.sc.intel.com><20050729055308.GA4200@Krystal>

Mathieu Desnoyers <compudj@krystal.dyndns.org> writes:
> 
> And as the jmp instruction is 5 bytes, there seems to be no hope to find an
> atomic operation that will write that.

Any 64bit architecture can write 8 bytes mostly atomically (at least towards
readers) and many 32bit architectures (like newer x86 with cmpxchg or sse) 
can too.

An 8 byte read-modify-store is not protected against multiple writers,
but that is no problem for probes which can protect against that
with a different lock.

x86 could actually do it atomically even for writers with cmpxchg8.

-Andi

Follow-Ups:
- Re: Hitachi djprobe mechanism
  - From: Richard J Moore
- Re: Hitachi djprobe mechanism
  - From: Mathieu Desnoyers

References:
- RE: Hitachi djprobe mechanism
  - From: Keshavamurthy, Anil S
- Re: Hitachi djprobe mechanism
  - From: Karim Yaghmour
- Re: Hitachi djprobe mechanism
  - From: Karim Yaghmour
- Re: Hitachi djprobe mechanism
  - From: Masami Hiramatsu
- Re: Hitachi djprobe mechanism
  - From: Karim Yaghmour
- Re: Hitachi djprobe mechanism
  - From: Mathieu Desnoyers
- Re: Hitachi djprobe mechanism
  - From: Mathieu Desnoyers
- Re: Hitachi djprobe mechanism
  - From: Mathieu Desnoyers

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