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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>
Cc: David Miller <davem@davemloft.net>,
	hch@infradead.org, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com,
	linux-arm-kernel@lists.infradead.org,
	linux-parisc@vger.kernel.org
Subject: Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap()
Date: Tue, 12 Mar 2019 08:46:50 -0700	[thread overview]
Message-ID: <1552405610.3083.17.camel@HansenPartnership.com> (raw)
In-Reply-To: <20190312075033-mutt-send-email-mst@kernel.org>

On Tue, 2019-03-12 at 07:54 -0400, Michael S. Tsirkin wrote:
> On Tue, Mar 12, 2019 at 03:17:00PM +0800, Jason Wang wrote:
> > 
> > On 2019/3/12 上午11:52, Michael S. Tsirkin wrote:
> > > On Tue, Mar 12, 2019 at 10:59:09AM +0800, Jason Wang wrote:
[...]
> > At least for -stable, we need the flush?
> > 
> > 
> > > Three atomic ops per bit is way to expensive.
> > 
> > 
> > Yes.
> > 
> > Thanks
> 
> See James's reply - I stand corrected we do kunmap so no need to
> flush.

Well, I said that's what we do on Parisc.  The cachetlb document
definitely says if you alter the data between kmap and kunmap you are
responsible for the flush.  It's just that flush_dcache_page() is a no-
op on x86 so they never remember to add it and since it will crash
parisc if you get it wrong we finally gave up trying to make them.

But that's the point: it is a no-op on your favourite architecture so
it costs you nothing to add it.

James


  reply	other threads:[~2019-03-12 15:46 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-06  7:18 [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Jason Wang
2019-03-06  7:18 ` [RFC PATCH V2 1/5] vhost: generalize adding used elem Jason Wang
2019-03-06  7:18 ` [RFC PATCH V2 2/5] vhost: fine grain userspace memory accessors Jason Wang
2019-03-06 10:45   ` Christophe de Dinechin
2019-03-07  2:38     ` Jason Wang
2019-03-06  7:18 ` [RFC PATCH V2 3/5] vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch() Jason Wang
2019-03-06  7:18 ` [RFC PATCH V2 4/5] vhost: introduce helpers to get the size of metadata area Jason Wang
2019-03-06 10:56   ` Christophe de Dinechin
2019-03-07  2:40     ` Jason Wang
2019-03-06 18:43   ` Souptick Joarder
2019-03-07  2:42     ` Jason Wang
2019-03-06  7:18 ` [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address Jason Wang
2019-03-06 16:31   ` Michael S. Tsirkin
2019-03-07  2:45     ` Jason Wang
2019-03-07 15:34       ` Michael S. Tsirkin
2019-03-07 19:09         ` Jerome Glisse
2019-03-07 19:38           ` Andrea Arcangeli
2019-03-07 20:17             ` Jerome Glisse
2019-03-07 21:27               ` Andrea Arcangeli
2019-03-08  9:13                 ` Jason Wang
2019-03-08 19:11                   ` Andrea Arcangeli
2019-03-11  7:21                     ` Jason Wang
2019-03-11 14:45                 ` Jan Kara
2019-03-08  8:31         ` Jason Wang
2019-03-07 15:47   ` Michael S. Tsirkin
2019-03-07 17:56     ` Michael S. Tsirkin
2019-03-07 19:16       ` Andrea Arcangeli
2019-03-08  8:50         ` Jason Wang
2019-03-08 14:58           ` Jerome Glisse
2019-03-11  7:18             ` Jason Wang
2019-03-08 19:48           ` Andrea Arcangeli
2019-03-08 20:06             ` Jerome Glisse
2019-03-11  7:40             ` Jason Wang
2019-03-11 12:48               ` Michael S. Tsirkin
2019-03-11 13:43                 ` Andrea Arcangeli
2019-03-12  2:56                   ` Jason Wang
2019-03-12  3:51                     ` Michael S. Tsirkin
2019-03-12  2:52                 ` Jason Wang
2019-03-12  3:50                   ` Michael S. Tsirkin
2019-03-12  7:15                     ` Jason Wang
2019-03-07 19:17       ` Jerome Glisse
2019-03-08  2:21         ` Michael S. Tsirkin
2019-03-08  2:55           ` Jerome Glisse
2019-03-08  3:16             ` Michael S. Tsirkin
2019-03-08  3:40               ` Jerome Glisse
2019-03-08  3:43                 ` Michael S. Tsirkin
2019-03-08  3:45                   ` Jerome Glisse
2019-03-08  9:15                     ` Jason Wang
2019-03-08  8:58         ` Jason Wang
2019-03-08 12:56           ` Michael S. Tsirkin
2019-03-08 15:02             ` Jerome Glisse
2019-03-08 19:13           ` Andrea Arcangeli
2019-03-08 14:12 ` [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Christoph Hellwig
2019-03-11  7:13   ` Jason Wang
2019-03-11 13:59     ` Michael S. Tsirkin
2019-03-11 18:14       ` David Miller
2019-03-12  2:59         ` Jason Wang
2019-03-12  3:52           ` Michael S. Tsirkin
2019-03-12  7:17             ` Jason Wang
2019-03-12 11:54               ` Michael S. Tsirkin
2019-03-12 15:46                 ` James Bottomley [this message]
2019-03-12 20:04                   ` Andrea Arcangeli
2019-03-12 20:53                     ` James Bottomley
2019-03-12 21:11                       ` Andrea Arcangeli
2019-03-12 21:19                         ` James Bottomley
2019-03-12 21:53                           ` Andrea Arcangeli
2019-03-12 22:02                             ` James Bottomley
2019-03-12 22:50                               ` Andrea Arcangeli
2019-03-12 22:57                                 ` James Bottomley
2019-03-13 16:05                       ` Christoph Hellwig
2019-03-13 16:37                         ` James Bottomley
2019-03-14 10:42                           ` Michael S. Tsirkin
2019-03-14 13:49                             ` Jason Wang
2019-03-14 19:33                               ` Andrea Arcangeli
2019-03-15  4:39                                 ` Jason Wang
2019-03-12  5:14           ` James Bottomley
2019-03-12  7:51             ` Jason Wang
2019-03-12  7:53               ` Jason Wang

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