From: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: kexec@lists.infradead.org, Cliff Wickman <cpw@sgi.com>
Subject: Re: 32TB kdump
Date: Mon, 01 Jul 2013 09:55:53 +0900 [thread overview]
Message-ID: <51D0D399.1070501@jp.fujitsu.com> (raw)
In-Reply-To: <20130627211725.GM4899@redhat.com>
(2013/06/28 6:17), Vivek Goyal wrote:
> On Fri, Jun 21, 2013 at 09:17:14AM -0500, Cliff Wickman wrote:
>
> Try using snappy or lzo for faster compression.
>
>> So a good workaround for a very large system might be to dump uncompressed
>> to an SSD.
>
> Interesting.
>
>> The multi-threading of the crash kernel would produce a big gain.
>
> Hatayama once was working on patches to bring up multiple cpus in second
> kernel. Not sure what happened to those patches.
>
>> - Use of mmap on /proc/vmcore increased page scanning speed from 4.4 minutes
>> to 3 minutes. It also increased data copying speed (unexpectedly) from
>> 38min. to 35min.
>
> Hmm.., so on large memory systems, mmap() will not help a lot? In those
> systems dump times are dominidated by disk speed and compression time.
>
> So far I was thinking that ioremap() per page was big issue and you
> also once had done the analysis that passing page list to kernel made
> things significantly faster.
>
> So on 32TB machines if it is taking 2hrs to save dump and mmap() shortens
> it by only few minutes, it really is not significant win.
>
Sorry, I've explained this earlier in this ML.
Some patches have been applied on makedumpfile to improve the filtering speed.
Two changes that were useful for the improvement are the one implementing
a 8-slot cache for physical page for the purpose of reducing the number of
/proc/vmcore access for paging (just as TLB), and the one that cleanups
makedumpfile's filtering path.
Performance degradation by ioremap() is now being hided on a single cpu, but
it would again occur on multiple cpus. Sorry, but I have yet to do benchmark
showing the fact cleanly as numeral values.
--
Thanks.
HATAYAMA, Daisuke
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next prev parent reply other threads:[~2013-07-01 0:56 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-21 14:17 32TB kdump Cliff Wickman
2013-06-27 21:17 ` Vivek Goyal
2013-06-28 21:56 ` Cliff Wickman
2013-07-01 0:42 ` HATAYAMA Daisuke
2013-07-01 2:57 ` Atsushi Kumagai
2013-07-01 16:12 ` Vivek Goyal
2013-07-01 0:55 ` HATAYAMA Daisuke [this message]
2013-07-01 16:06 ` Vivek Goyal
[not found] ` <51D3D15D.5090600@jp.fujitsu.com>
2013-07-03 13:03 ` Vivek Goyal
2013-07-04 2:03 ` HATAYAMA Daisuke
2013-07-05 15:21 ` Not booting BSP in kdump kernel (Was: Re: 32TB kdump) Vivek Goyal
2013-07-08 9:23 ` HATAYAMA Daisuke
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