From 394313fff39d0f994325c47f7eab39daf5dc9e11 Mon Sep 17 00:00:00 2001 From: Maxime Coquelin Date: Wed, 21 Mar 2018 16:44:13 +0100 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 Reviewed-by: Jianfeng Tan --- 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 58aec2e0d8..7ca2a03079 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 -- 2.20.1