From: Jason Wang <jasowang@redhat.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>,
David Miller <davem@davemloft.net>,
mst@redhat.com
Cc: 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 15:53:37 +0800 [thread overview]
Message-ID: <7f779c16-58d1-dd4f-54cf-a7538d4b6fe4@redhat.com> (raw)
In-Reply-To: <f9e52313-0a06-22b6-140c-ded75eecde20@redhat.com>
On 2019/3/12 下午3:51, Jason Wang wrote:
>
> On 2019/3/12 下午1:14, James Bottomley wrote:
>> On Tue, 2019-03-12 at 10:59 +0800, Jason Wang wrote:
>>> On 2019/3/12 上午2:14, David Miller wrote:
>>>> From: "Michael S. Tsirkin" <mst@redhat.com>
>>>> Date: Mon, 11 Mar 2019 09:59:28 -0400
>>>>
>>>>> On Mon, Mar 11, 2019 at 03:13:17PM +0800, Jason Wang wrote:
>>>>>> On 2019/3/8 下午10:12, Christoph Hellwig wrote:
>>>>>>> On Wed, Mar 06, 2019 at 02:18:07AM -0500, Jason Wang wrote:
>>>>>>>> This series tries to access virtqueue metadata through
>>>>>>>> kernel virtual
>>>>>>>> address instead of copy_user() friends since they had too
>>>>>>>> much
>>>>>>>> overheads like checks, spec barriers or even hardware
>>>>>>>> feature
>>>>>>>> toggling. This is done through setup kernel address through
>>>>>>>> vmap() and
>>>>>>>> resigter MMU notifier for invalidation.
>>>>>>>>
>>>>>>>> Test shows about 24% improvement on TX PPS. TCP_STREAM
>>>>>>>> doesn't see
>>>>>>>> obvious improvement.
>>>>>>> How is this going to work for CPUs with virtually tagged
>>>>>>> caches?
>>>>>> Anything different that you worry?
>>>>> If caches have virtual tags then kernel and userspace view of
>>>>> memory
>>>>> might not be automatically in sync if they access memory
>>>>> through different virtual addresses. You need to do things like
>>>>> flush_cache_page, probably multiple times.
>>>> "flush_dcache_page()"
>>>
>>> I get this. Then I think the current set_bit_to_user() is suspicious,
>>> we
>>> probably miss a flush_dcache_page() there:
>>>
>>>
>>> static int set_bit_to_user(int nr, void __user *addr)
>>> {
>>> unsigned long log = (unsigned long)addr;
>>> struct page *page;
>>> void *base;
>>> int bit = nr + (log % PAGE_SIZE) * 8;
>>> int r;
>>>
>>> r = get_user_pages_fast(log, 1, 1, &page);
>>> if (r < 0)
>>> return r;
>>> BUG_ON(r != 1);
>>> base = kmap_atomic(page);
>>> set_bit(bit, base);
>>> kunmap_atomic(base);
>> This sequence should be OK. get_user_pages() contains a flush which
>> clears the cache above the user virtual address, so on kmap, the page
>> is coherent at the new alias. On parisc at least, kunmap embodies a
>> flush_dcache_page() which pushes any changes in the cache above the
>> kernel virtual address back to main memory and makes it coherent again
>> for the user alias to pick it up.
>
>
> It would be good if kmap()/kunmap() can do this but looks like we can
> not assume this? For example, sparc's flush_dcache_page()
Sorry, I meant kunmap_atomic().
Thanks
> doesn't do flush_dcache_page(). And bio_copy_data_iter() do
> flush_dcache_page() after kunmap_atomic().
>
> Thanks
>
>
>>
>> James
>>
>
prev parent reply other threads:[~2019-03-12 7:53 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
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 [this message]
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