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To: luca.boccassi@gmail.com
Cc: Jianfeng Tan <jianfeng.tan@intel.com>, dpdk stable <stable@dpdk.org>
References: <20180430140606.4615-80-luca.boccassi@gmail.com>
<20180430144223.18657-1-luca.boccassi@gmail.com>
<20180430144223.18657-5-luca.boccassi@gmail.com>
From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Date: Mon, 30 Apr 2018 16:44:49 +0200
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Subject: Re: [dpdk-stable] patch 'vhost: avoid concurrency when logging
dirty pages' has been queued to stable release 18.02.2
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Hi Luca,
Please don't backport this patch to -stable releases.
It has already been reverted in upstream master, and a new patch is to
be posted in the coming hours.
I already notified Yuanhan for the same for v17.11 LTS.
Thanks,
Maxime
On 04/30/2018 04:40 PM, luca.boccassi@gmail.com wrote:
> Hi,
>
> FYI, your patch has been queued to stable release 18.02.2
>
> Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
> It will be pushed if I get no objections before 05/02/18. So please
> shout if anyone has objections.
>
> Thanks.
>
> Luca Boccassi
>
> ---
> From a5d642c446cc3a3be41694715d99f3e9f9ea44df Mon Sep 17 00:00:00 2001
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Date: Wed, 21 Mar 2018 16:44:13 +0100
> Subject: [PATCH] vhost: avoid concurrency when logging dirty pages
>
> [ upstream commit 394313fff39d0f994325c47f7eab39daf5dc9e11 ]
>
> This patch aims at fixing a migration performance regression
> faced since atomic operation is used to log pages as dirty when
> doing live migration.
>
> Instead of setting a single bit by doing an atomic read-modify-write
> operation to log a page as dirty, this patch write 0xFF to the
> corresponding byte, and so logs 8 page as dirty.
>
> The advantage is that it avoids concurrent atomic operations by
> multiple PMD threads, the drawback is that some clean pages are
> marked as dirty and so are transferred twice.
>
> Fixes: 897f13a1f726 ("vhost: make page logging atomic")
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> Reviewed-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
> lib/librte_vhost/vhost.h | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index bab0b456e..a4f23f714 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -247,18 +247,14 @@ struct virtio_net {
> #define VHOST_LOG_PAGE 4096
>
> /*
> - * Atomically set a bit in memory.
> + * Mark all pages belonging to the same dirty log bitmap byte
> + * as dirty. The goal is to avoid concurrency between different
> + * threads doing atomic read-modify-writes on the same byte.
> */
> -static __rte_always_inline void
> -vhost_set_bit(unsigned int nr, volatile uint8_t *addr)
> -{
> - __sync_fetch_and_or_8(addr, (1U << nr));
> -}
> -
> static __rte_always_inline void
> vhost_log_page(uint8_t *log_base, uint64_t page)
> {
> - vhost_set_bit(page % 8, &log_base[page / 8]);
> + log_base[page / 8] = 0xff;
> }
>
> static __rte_always_inline void
>