From bb77d555d4c422d987b492f6ee6c0533a6486d4e Mon Sep 17 00:00:00 2001 From: Maxime Coquelin Date: Fri, 20 Apr 2018 10:39:21 +0200 Subject: [PATCH] vhost: revert avoid concurrency when logging dirty pages This reverts commit 394313fff39d0f994325c47f7eab39daf5dc9e11. While the patch did solve concurrency issue, it induces more pages copies as some clean pages are marked as dirty for performance reasons. Moreover, as there is no more contention doing the logging, the rate of packets than can be processed is higher, leading to even more pages to be dirtied. It has been reported that with more than one queue pair, and with a relatively low packet rate (1Mpps), the live migration never converges until the flow is stopped. While a better solution is found, it is better to reset to the old behaviour, i.e. using atomic operation for dirty pages logging. Signed-off-by: Maxime Coquelin --- lib/librte_vhost/vhost.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h index ba2fc74048..8919781313 100644 --- a/lib/librte_vhost/vhost.h +++ b/lib/librte_vhost/vhost.h @@ -304,14 +304,18 @@ struct virtio_net { #define VHOST_LOG_PAGE 4096 /* - * 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. + * Atomically set a bit in memory. */ +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) { - log_base[page / 8] = 0xff; + vhost_set_bit(page % 8, &log_base[page / 8]); } static __rte_always_inline void -- 2.20.1