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From: Yuanhan Liu <yliu@fridaylinux.org>
To: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: dev@dpdk.org, jfreiman@redhat.com, tiwei.bie@intel.com,
	mst@redhat.com, vkaplans@redhat.com, jasowang@redhat.com
Subject: Re: [dpdk-dev] [PATCH 21/21] vhost: iotlb: reduce iotlb read lock usage
Date: Mon, 11 Sep 2017 12:18:21 +0800	[thread overview]
Message-ID: <20170911041821.GI9736@yliu-home> (raw)
In-Reply-To: <20170831095023.21037-22-maxime.coquelin@redhat.com>

On Thu, Aug 31, 2017 at 11:50:23AM +0200, Maxime Coquelin wrote:
> Prior to this patch, iotlb cache's read/write lock was
> read-locked at every guest IOVA to app VA translation,
> i.e. at least once per packet with indirect off and twice
> with indirect on.
> 
> The problem is that rte_rwlock_read_lock() makes use of atomic
> operation, which is costly.
> 
> This patch introduces iotlb lock helpers, so that a full burst
> can be protected with taking the lock once, which reduces the
> number of atomic operations by up to 64 with indirect
> descriptors.

You were assuming there is no single miss during a burst. If a miss
happens, it requries 2 locks: one for _pending_miss and another one
for _pending_insert. From this point of view, it's actually more
expensive.

However, I won't call it's a bad assumption (for the case of virtio
PMD). And if you take this assumption, why not just deleting the
pending list and moving the lock outside the _iotlb_find function()
like what you did in this patch?

I don't really see the point of introducing the pending list.

	--yliu

  reply	other threads:[~2017-09-11  4:18 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-31  9:50 [dpdk-dev] [PATCH 00/21] Vhost-user: Implement device IOTLB support Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 01/21] Revert "vhost: workaround MQ fails to startup" Maxime Coquelin
2017-09-07 11:54   ` Yuanhan Liu
2017-09-07 12:59     ` Maxime Coquelin
2017-09-24 10:41       ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 02/21] vhost: make error handling consistent in rx path Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 03/21] vhost: protect virtio_net device struct Maxime Coquelin
2017-09-05  4:45   ` Tiwei Bie
2017-09-05  9:24     ` Maxime Coquelin
2017-09-05 10:07       ` Tiwei Bie
2017-09-05 11:00         ` Maxime Coquelin
2017-09-06  1:15           ` Tiwei Bie
2017-09-06  2:59             ` Stephen Hemminger
2017-09-06  7:50               ` Maxime Coquelin
2017-09-06  7:15             ` Maxime Coquelin
2017-09-06  7:30               ` Tiwei Bie
2017-09-06 20:02                 ` Maxime Coquelin
2017-09-07  5:08                   ` Tiwei Bie
2017-09-07 13:44   ` Yuanhan Liu
2017-09-07 14:01     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 04/21] vhost: prepare send_vhost_message() to slave requests Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 05/21] vhost: add support to slave requests channel Maxime Coquelin
2017-09-05  4:19   ` Tiwei Bie
2017-09-05  8:18     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 06/21] vhost: declare missing IOMMU-related definitions for old kernels Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 07/21] vhost: add iotlb helper functions Maxime Coquelin
2017-09-05  6:02   ` Tiwei Bie
2017-09-05 15:16     ` Maxime Coquelin
2017-09-08  8:08   ` Yuanhan Liu
2017-09-08  8:24     ` Maxime Coquelin
2017-09-08  8:36       ` Yuanhan Liu
2017-09-08  8:50         ` Maxime Coquelin
2017-09-08  9:21           ` Yuanhan Liu
2017-09-08  9:28             ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 08/21] vhost: iotlb: add pending miss request list and helpers Maxime Coquelin
2017-09-05  7:11   ` Tiwei Bie
2017-09-05 15:18     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 09/21] vhost-user: add support to IOTLB miss slave requests Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 10/21] vhost: initialize vrings IOTLB caches Maxime Coquelin
2017-09-04 13:57   ` Remy Horton
2017-09-04 15:45     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 11/21] vhost-user: handle IOTLB update and invalidate requests Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 12/21] vhost: introduce guest IOVA to backend VA helper Maxime Coquelin
2017-09-05  4:14   ` Tiwei Bie
2017-09-05  7:05     ` Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 13/21] vhost: use the guest IOVA to host " Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 14/21] vhost: enable rings at the right time Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 15/21] vhost: don't dereference invalid dev pointer after its reallocation Maxime Coquelin
2017-09-04 13:58   ` Remy Horton
2017-08-31  9:50 ` [dpdk-dev] [PATCH 16/21] vhost: postpone rings addresses translation Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 17/21] vhost-user: translate ring addresses when IOMMU enabled Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 18/21] vhost-user: iommu: postpone device creation until ring are mapped Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 19/21] vhost: iommu: Invalidate vring in case of matching IOTLB invalidate Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 20/21] vhost: enable IOMMU support Maxime Coquelin
2017-08-31  9:50 ` [dpdk-dev] [PATCH 21/21] vhost: iotlb: reduce iotlb read lock usage Maxime Coquelin
2017-09-11  4:18   ` Yuanhan Liu [this message]
2017-09-11  7:34     ` Maxime Coquelin
2017-09-11  9:39       ` Yuanhan Liu
2017-09-04 13:58 ` [dpdk-dev] [PATCH 00/21] Vhost-user: Implement device IOTLB support Remy Horton

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