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From: Pratyush Anand <panand@redhat.com>
To: James Morse <james.morse@arm.com>
Cc: Geoff Levand <geoff@infradead.org>,
	kexec@lists.infradead.org, Simon Horman <horms@verge.net.au>,
	Vivek Goyal <vgoyal@redhat.com>,
	Petitboot@lists.ozlabs.org, Scott Wood <scottwood@freescale.com>,
	Dave Young <dyoung@redhat.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] kexec: Add --lite option
Date: Mon, 7 Dec 2015 19:37:55 +0530	[thread overview]
Message-ID: <20151207140755.GG16406@dhcppc13.redhat.com> (raw)
In-Reply-To: <56658696.6070103@arm.com>

Hi James,

Thanks for the reply.

On 07/12/2015:01:16:06 PM, James Morse wrote:
> Hi Pratyush,
> 
> On 07/12/15 11:48, Pratyush Anand wrote:
> >> 1) When we execute kexec() system call in first kernel, at that time it
> >> calculates sha256 on all the binaries [1]. It take almost un-noticeable time
> >> (less than a sec) there.
> >>
> >> 2) When purgatory is executed then it re-calculates sha256 using same routines
> >> [2] on same binary data as that of case (1). But, now it takes 10-20 sec
> >> (depending of size of binaries)?
> >>
> >> Why did not it take same time with O2 + D-cache enabled? I think, we should be
> >> able to achieve same time in second case as well. What is missing?
> 
> I haven't benchmarked this, but:
> 
> util_lib/sha256.c contains calls out to memcpy().
> In your case 1, this will use the glibc version. In case 2, it will use
> the version implemented in purgatory/string.c, which is a byte-by-byte copy.
> 

Yes, I agree that byte copy is too slow. But, memcpy() in sha256_update() will
copy only few bytes (I think max 126 bytes). Most of the data will be processed
using loop while( length >= 64 ){}, where we do not have any memcpy.So, I do not
think that this would be causing such a difference.

Could it be the case that I am not using perfect memory attributes while setting
up identity mapping and enabling D-cache. My implementation is here:
https://github.com/pratyushanand/kexec-tools/commit/8efdbc56b52f99a8a074edd0ddc519d7b68be82f

~Pratyush

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec

WARNING: multiple messages have this Message-ID (diff)
From: panand@redhat.com (Pratyush Anand)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] kexec: Add --lite option
Date: Mon, 7 Dec 2015 19:37:55 +0530	[thread overview]
Message-ID: <20151207140755.GG16406@dhcppc13.redhat.com> (raw)
In-Reply-To: <56658696.6070103@arm.com>

Hi James,

Thanks for the reply.

On 07/12/2015:01:16:06 PM, James Morse wrote:
> Hi Pratyush,
> 
> On 07/12/15 11:48, Pratyush Anand wrote:
> >> 1) When we execute kexec() system call in first kernel, at that time it
> >> calculates sha256 on all the binaries [1]. It take almost un-noticeable time
> >> (less than a sec) there.
> >>
> >> 2) When purgatory is executed then it re-calculates sha256 using same routines
> >> [2] on same binary data as that of case (1). But, now it takes 10-20 sec
> >> (depending of size of binaries)?
> >>
> >> Why did not it take same time with O2 + D-cache enabled? I think, we should be
> >> able to achieve same time in second case as well. What is missing?
> 
> I haven't benchmarked this, but:
> 
> util_lib/sha256.c contains calls out to memcpy().
> In your case 1, this will use the glibc version. In case 2, it will use
> the version implemented in purgatory/string.c, which is a byte-by-byte copy.
> 

Yes, I agree that byte copy is too slow. But, memcpy() in sha256_update() will
copy only few bytes (I think max 126 bytes). Most of the data will be processed
using loop while( length >= 64 ){}, where we do not have any memcpy.So, I do not
think that this would be causing such a difference.

Could it be the case that I am not using perfect memory attributes while setting
up identity mapping and enabling D-cache. My implementation is here:
https://github.com/pratyushanand/kexec-tools/commit/8efdbc56b52f99a8a074edd0ddc519d7b68be82f

~Pratyush

  reply	other threads:[~2015-12-07 14:07 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-21 23:12 [PATCH] kexec: Add --lite option Geoff Levand
2015-10-22  0:02 ` Jeremy Kerr
2015-10-22  0:37   ` Geoff Levand
2015-11-05  6:20     ` Scott Wood
2015-10-22  3:17 ` Dave Young
2015-10-22 12:50   ` Vivek Goyal
2015-10-22 19:08     ` Geoff Levand
2015-11-05  5:56       ` Scott Wood
2015-12-07 11:45         ` Pratyush Anand
2015-12-07 11:48           ` Pratyush Anand
2015-12-07 11:48             ` Pratyush Anand
2015-12-07 13:16             ` James Morse
2015-12-07 13:16               ` James Morse
2015-12-07 14:07               ` Pratyush Anand [this message]
2015-12-07 14:07                 ` Pratyush Anand
2015-12-08  1:03                 ` Scott Wood
2015-12-08  1:03                   ` Scott Wood
2015-12-08 16:00                 ` James Morse
2015-12-08 16:00                   ` James Morse
2015-12-09  9:28                   ` Pratyush Anand
2015-12-09  9:28                     ` Pratyush Anand
2016-01-11 12:46                     ` Pratyush Anand
2016-01-11 12:46                       ` Pratyush Anand
2016-01-12  1:06                       ` Simon Horman
2016-01-12  1:06                         ` Simon Horman
2015-10-22 18:57   ` Geoff Levand
2015-10-22 19:04     ` Vivek Goyal
2015-10-23  9:46     ` Dave Young
2015-10-23 18:49       ` Geoff Levand
2015-10-23 19:02     ` Eric W. Biederman
2018-04-11 18:30 ` [PATCH v2] kexec: Add --no-checks option Geoff Levand
2018-04-19  8:38   ` Simon Horman

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