To: renzo@cs.unibo.it (Renzo Davoli)
Cc: osd@cs.unibo.it, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2-ptrace_multi
References: <20060518155337.GA17498@cs.unibo.it>
	<20060518155848.GC17498@cs.unibo.it>
From: Andi Kleen <ak@suse.de>
Date: 18 May 2006 22:17:08 +0200
In-Reply-To: <20060518155848.GC17498@cs.unibo.it>
Message-ID: <p73sln72im3.fsf@bragg.suse.de>
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renzo@cs.unibo.it (Renzo Davoli) writes:

> ptmulti kernel patch inserts a new useful option for ptrace() call, 
> adding a new request type to ptrace() syscall.
> 
> With PTRACE_MULTI option you can send multiple ptrace requests with a 
> single system call: commonly a process that uses ptrace() needs
> several PTRACE_PEEKDATA for getting some useful, even small pieces of data.
> It is useful for these programs to run several ptrace
> operations while limiting the number of context switches.

What context switches do you mean?  System calls? Linux is in general
designed to have very cheap system calls and they shouldn't be more tha
a few hundred cycles. 

> 
> Debuggers and virtual machines (like User Mode Linux) and many other 
> applications that are based on ptrace can get great 
> performance improvements by PTRACE_MULTI: the number of system
> calls (and context switches) decreases significantly.

You forgot to add numbers? 

-Andi
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