From: Mikulas Patocka <mpatocka@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>,
device-mapper development <dm-devel@redhat.com>,
"Alasdair G. Kergon" <agk@redhat.com>,
Mike Snitzer <snitzer@redhat.com>,
linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: dm-writecache
Date: Fri, 18 May 2018 18:00:21 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.1805181755410.27649@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <CAPcyv4jecVBaJb5WeO3FdbJ8xabishbAccORoXN2pHKOvUc2qA@mail.gmail.com>
On Fri, 18 May 2018, Dan Williams wrote:
> >> ...and I wonder what the benefit is of the 16-byte case? I would
> >> assume the bulk of the benefit is limited to the 4 and 8 byte copy
> >> cases.
> >
> > dm-writecache uses 16-byte writes frequently, so it is needed for that.
> >
> > If we split 16-byte write to two 8-byte writes, it would degrade
> > performance for architectures where memcpy_flushcache needs to flush the
> > cache.
>
> My question was how measurable it is to special case 16-byte
> transfers? I know Ingo is going to ask this question, so it would
> speed things along if this patch included performance benefit numbers
> for each special case in the changelog.
I tested it some times ago - and the movnti instruction has 2% better
throughput than the existing memcpy_flushcache function.
It is doing one 16-byte write for every sector written and one 8-byte
write for every sector clean-up. So, the overhead is measurable.
Mikulas
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WARNING: multiple messages have this Message-ID (diff)
From: Mikulas Patocka <mpatocka-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
device-mapper development
<dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Alasdair G. Kergon"
<agk-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
linux-nvdimm
<linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org>
Subject: Re: dm-writecache
Date: Fri, 18 May 2018 18:00:21 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.1805181755410.27649@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <CAPcyv4jecVBaJb5WeO3FdbJ8xabishbAccORoXN2pHKOvUc2qA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Fri, 18 May 2018, Dan Williams wrote:
> >> ...and I wonder what the benefit is of the 16-byte case? I would
> >> assume the bulk of the benefit is limited to the 4 and 8 byte copy
> >> cases.
> >
> > dm-writecache uses 16-byte writes frequently, so it is needed for that.
> >
> > If we split 16-byte write to two 8-byte writes, it would degrade
> > performance for architectures where memcpy_flushcache needs to flush the
> > cache.
>
> My question was how measurable it is to special case 16-byte
> transfers? I know Ingo is going to ask this question, so it would
> speed things along if this patch included performance benefit numbers
> for each special case in the changelog.
I tested it some times ago - and the movnti instruction has 2% better
throughput than the existing memcpy_flushcache function.
It is doing one 16-byte write for every sector written and one 8-byte
write for every sector clean-up. So, the overhead is measurable.
Mikulas
next prev parent reply other threads:[~2018-05-18 22:00 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-08 13:25 [PATCH] dm-writecache Mikulas Patocka
2018-03-08 14:51 ` [dm-devel] " Christoph Hellwig
2018-03-08 14:51 ` Christoph Hellwig
2018-03-08 17:08 ` Dan Williams
2018-03-08 17:08 ` Dan Williams
2018-03-12 7:48 ` Christoph Hellwig
2018-03-12 7:48 ` Christoph Hellwig
2018-03-12 12:15 ` Mikulas Patocka
2018-03-12 12:15 ` Mikulas Patocka
2018-05-18 15:44 ` dm-writecache Mike Snitzer
2018-05-18 15:44 ` dm-writecache Mike Snitzer
2018-05-18 15:54 ` dm-writecache Dan Williams
2018-05-18 15:54 ` dm-writecache Dan Williams
2018-05-18 20:12 ` dm-writecache Mikulas Patocka
2018-05-18 20:12 ` dm-writecache Mikulas Patocka
2018-05-18 20:14 ` dm-writecache Dan Williams
2018-05-18 20:14 ` dm-writecache Dan Williams
2018-05-18 22:00 ` Mikulas Patocka [this message]
2018-05-18 22:00 ` dm-writecache Mikulas Patocka
2018-05-18 22:10 ` dm-writecache Dan Williams
2018-05-18 22:10 ` dm-writecache Dan Williams
2018-03-09 3:26 ` [dm-devel] [PATCH] dm-writecache Mikulas Patocka
2018-03-09 3:26 ` Mikulas Patocka
2018-03-12 7:50 ` Christoph Hellwig
2018-03-12 7:50 ` Christoph Hellwig
2018-03-12 12:12 ` Mikulas Patocka
2018-03-12 12:12 ` Mikulas Patocka
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