linux-kernel - Re: [PATCH] x86, efi: Break up large initrd reads

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Message-ID: <4EE689D5.4070600@zytor.com>
Date:	Mon, 12 Dec 2011 15:10:13 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matt Fleming <matt@...sole-pimps.org>
CC:	Maarten Lankhorst <m.b.lankhorst@...il.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Matthew Garrett <mjg@...hat.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Mike Waychison <mikew@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Jones <pjones@...hat.com>
Subject: Re: [PATCH] x86, efi: Break up large initrd reads

On 11/25/2011 12:48 AM, Matt Fleming wrote:
> On Fri, 2011-11-25 at 02:37 +0100, Maarten Lankhorst wrote:
>> The efi boot stub tries to read the entire initrd in 1 go,
>> however some efi implementations hang if too much if asked
>> to read too much data at the same time. After some
>> experimentation I found out that my asrock p67 board will
>> hang if asked to read chunks of 4mb, so use a safe value.
>>
>> From elilo source code:
>> /*
>>  * We load by chunks rather than a single big read because
>>  * early versions of EFI had troubles loading files
>>  * from floppies in a single big request.  Breaking
>>  * the read down into chunks of 4KB fixed that
>>  * problem. While this problem has been fixed, we still prefer
>>  * this method because it tells us whether or not we're making
>>  * forward progress.
>>  */
>>
>> While the comment says 4KB, it's using 4 * EFI_PAGE_SIZE (16KB),
>> so I went by the safest route of following elilo here.
>>

I'm going to NAK this, because I think the performance impact is too
severe.  I would like to set the cap at 1 MiB for now, unless we can
identify platforms where *that* is known to fail.

Maarten, would you be willing to rev your patch?  Furthermore, please
make the maximum chunksize a define.

	-hpa

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