[dpdk-stable] [PATCH v16.11 LTS] vhost: improve dirty pages logging performance

[Luca Boccassi]

On Wed, 2018-05-23 at 09:53 +0200, Maxime Coquelin wrote:
> [ upstream commit c16915b8710911a75f0fbdb1aa5243f4cdfaf26a ]
> 
> This patch caches all dirty pages logging until the used ring index
> is updated.
> 
> The goal of this optimization is to fix a performance regression
> introduced when the vhost library started to use atomic operations
> to set bits in the shared dirty log map. While the fix was valid
> as previous implementation wasn't safe against concurrent accesses,
> contention was induced.
> 
> With this patch, during migration, we have:
> 1. Less atomic operations as only a single atomic OR operation
> per 32 or 64 (depending on CPU) pages.
> 2. Less atomic operations as during a burst, the same page will
> be marked dirty only once.
> 3. Less write memory barriers.
> 
> Fixes: 897f13a1f726 ("vhost: make page logging atomic")
> Cc: stable at dpdk.org
> 
> Suggested-by: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
> Reviewed-by: Tiwei Bie <tiwei.bie at intel.com>
> ---
> 
> Hi,
> 
> This backport had some conflicts, mainly because the dirty pages
> logging functions moved from virtio-net.c to vhost.h after 16.11.
> 
> Main other change with upstream is the GCC_VERSION isn't defined,
> so I decided to remove the optimization done for GCC >= 7.1 as it
> is unlikely to be used with v16.11 LTS.
> 
> To test it, I had to revert 357f27736c79d as vhost is currently
> broken on 16.11 branch (see separate mail).
> 
>  lib/librte_vhost/vhost.h      |  13 +++++
>  lib/librte_vhost/virtio_net.c | 128
> +++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 126 insertions(+), 15 deletions(-)

Thanks, applied and pushed to 16.11.

-- 
Kind regards,
Luca Boccassi