From: Vlastimil Babka <vbabka@suse.cz>
To: Will Deacon <will@kernel.org>
Cc: Prathu Baronia <prathu.baronia@oneplus.com>,
catalin.marinas@arm.com, alexander.duyck@gmail.com,
chintan.pandya@oneplus.com, mhocko@suse.com,
akpm@linux-foundation.org, linux-mm@kvack.org,
gregkh@linuxfoundation.com, gthelen@google.com, jack@suse.cz,
ken.lin@oneplus.com, gasine.xu@oneplus.com, ying.huang@intel.com,
mark.rutland@arm.com
Subject: Re: [PATCH v2] mm: Optimized hugepage zeroing & copying from user
Date: Tue, 21 Apr 2020 15:48:04 +0200 [thread overview]
Message-ID: <5e334947-22e9-e59d-f7bb-63e04cc8caf0@suse.cz> (raw)
In-Reply-To: <20200421133935.GC17875@willie-the-truck>
On 4/21/20 3:39 PM, Will Deacon wrote:
> On Tue, Apr 21, 2020 at 02:48:04PM +0200, Vlastimil Babka wrote:
>> On 4/21/20 2:47 PM, Vlastimil Babka wrote:
>> >
>> > It was suspected that current Intel can prefetch forward and backwards, and the
>> > tested ARM64 microarchitecture only backwards, can it be true? The current code
>>
>> Oops, tested ARM64 microarchitecture I meant "only forwards".
>
> I'd be surprised if that's the case, but it could be that there's an erratum
> workaround in play which hampers the prefetch behaviour. We generally try
> not to assume too much about the prefetcher on arm64 because they're not
> well documented and vary wildly between different micro-architectures.
Yeah it's probably not as simple as I thought, as the test code [1] shows the
page iteration goes backwards, but per-page memsets are not special. So maybe
it's not hardware specifics, but x86 memtest implementation is also done
backwards, so it fits the backwards outer loop, but arm64 memset is forward, so
the resulting pattern is non-linear?
In that case it's also a question if the measurement was done in kernel or
userspace, and if userspace memset have any implications for kernel memset...
[1] https://lore.kernel.org/linux-mm/20200414153829.GA15230@oneplus.com/
> Will
>
next prev parent reply other threads:[~2020-04-21 13:48 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 15:38 [PATCH v2] mm: Optimized hugepage zeroing & copying from user Prathu Baronia
2020-04-14 17:03 ` Michal Hocko
2020-04-14 17:41 ` Daniel Jordan
[not found] ` <20200414184743.GB2097@oneplus.com>
2020-04-14 19:32 ` Alexander Duyck
2020-04-15 3:40 ` Huang, Ying
2020-04-15 11:09 ` Michal Hocko
2020-04-19 12:05 ` Prathu Baronia
2020-04-14 19:40 ` Michal Hocko
2020-04-15 3:27 ` Huang, Ying
2020-04-16 1:21 ` Huang, Ying
2020-04-19 15:58 ` Prathu Baronia
2020-04-20 0:18 ` Huang, Ying
2020-04-21 9:36 ` Prathu Baronia
2020-04-21 10:09 ` Will Deacon
2020-04-21 12:47 ` Vlastimil Babka
2020-04-21 12:48 ` Vlastimil Babka
2020-04-21 13:39 ` Will Deacon
2020-04-21 13:48 ` Vlastimil Babka [this message]
2020-04-21 13:56 ` Chintan Pandya
2020-04-22 8:18 ` Will Deacon
2020-04-22 11:19 ` Will Deacon
2020-04-22 14:38 ` Prathu Baronia
2020-05-01 8:58 ` Prathu Baronia
2020-05-05 8:59 ` Will Deacon
2020-04-21 13:00 ` Michal Hocko
2020-04-21 13:10 ` Will Deacon
2020-04-17 7:48 ` [mm] 134c8b410f: vm-scalability.median -7.9% regression kernel test robot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5e334947-22e9-e59d-f7bb-63e04cc8caf0@suse.cz \
--to=vbabka@suse.cz \
--cc=akpm@linux-foundation.org \
--cc=alexander.duyck@gmail.com \
--cc=catalin.marinas@arm.com \
--cc=chintan.pandya@oneplus.com \
--cc=gasine.xu@oneplus.com \
--cc=gregkh@linuxfoundation.com \
--cc=gthelen@google.com \
--cc=jack@suse.cz \
--cc=ken.lin@oneplus.com \
--cc=linux-mm@kvack.org \
--cc=mark.rutland@arm.com \
--cc=mhocko@suse.com \
--cc=prathu.baronia@oneplus.com \
--cc=will@kernel.org \
--cc=ying.huang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).