linux-kernel - Re: [RFC] [PATCH 00/19] Non disruptive application core dump infrastructure using task_work

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Message-ID: <20131007181018.GL6882@two.firstfloor.org>
Date:	Mon, 7 Oct 2013 20:10:18 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Suzuki K. Poulose" <suzuki@...ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Janani Venkataraman <jananive@...ibm.com>,
	linux-kernel@...r.kernel.org, amwang@...hat.com,
	rdunlap@...otime.net, aravinda@...ux.vnet.ibm.com, hch@....de,
	mhiramat@...hat.com, jeremy.fitzhardinge@...rix.com,
	xemul@...allels.com, suzuki@...ux.vnet.ibm.com,
	kosaki.motohiro@...fujitsu.com, adobriyan@...il.com,
	tarundsk@...ux.vnet.ibm.com, vapier@...too.org,
	roland@...k.frob.com, tj@...nel.org, ananth@...ux.vnet.ibm.com,
	gorcunov@...nvz.org, avagin@...nvz.org, oleg@...hat.com,
	eparis@...hat.com, d.hatayama@...fujitsu.com,
	james.hogan@...tec.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org
Subject: Re: [RFC] [PATCH 00/19] Non disruptive application core dump
 infrastructure using task_work_add()

> > Couldn't they just use the new process_vm_readv() syscalls instead?
> > AFAIK those do not require ptrace.
> > 
> We need the register set and hence would need a ptrace.

But the kernel needs to stop to to read the registers.

Do you have data how much the latency difference is between
an optimized ptrace reader (using PTRACE_GETREGSET) vs the kernel ?

-Andi
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