From: "Tan, Jianfeng" <jianfeng.tan@intel.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>,
"dev@dpdk.org" <dev@dpdk.org>, "Bie, Tiwei" <tiwei.bie@intel.com>,
"jfreimann@redhat.com" <jfreimann@redhat.com>
Cc: "stable@dpdk.org" <stable@dpdk.org>
Subject: Re: [dpdk-stable] [PATCH] vhost: avoid concurrency when logging dirty pages
Date: Tue, 27 Mar 2018 01:15:41 +0000 [thread overview]
Message-ID: <ED26CBA2FAD1BF48A8719AEF02201E36514A5FFD@SHSMSX103.ccr.corp.intel.com> (raw)
In-Reply-To: <20180321154413.1120-1-maxime.coquelin@redhat.com>
> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Wednesday, March 21, 2018 11:44 PM
> To: dev@dpdk.org; Tan, Jianfeng; Bie, Tiwei; jfreimann@redhat.com
> Cc: stable@dpdk.org; Maxime Coquelin
> Subject: [PATCH] vhost: avoid concurrency when logging dirty pages
>
> 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")
> Cc: stable@dpdk.org
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
As you mentioned, the concern is if it affects the rate of convergence. Hope we could have some tests on that.
Reviewed-by: Jianfeng Tan <jianfeng.tan@intel.com>
Thanks!
> ---
> 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 d947bc9e3..aa2606f8a 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
> --
> 2.14.3
next prev parent reply other threads:[~2018-03-27 1:15 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-21 15:44 Maxime Coquelin
2018-03-27 1:15 ` Tan, Jianfeng [this message]
2018-03-27 11:24 ` Maxime Coquelin
2018-03-30 7:42 ` Maxime Coquelin
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