From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-devel@nongnu.org
Cc: qemu-trivial@nongnu.org, cota@braap.org
Subject: [Qemu-devel] [PATCH] exec: avoid unnecessary cacheline bounce on ram_list.mru_block
Date: Thu, 22 Oct 2015 13:51:30 +0200 [thread overview]
Message-ID: <1445514690-7883-1-git-send-email-pbonzini@redhat.com> (raw)
Whenever the MRU cache hits for the list of RAM blocks, qemu_get_ram_block
does an unnecessary write that causes a processor cache line to bounce
from one core to another. This causes a performance hit.
Reported-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
exec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/exec.c b/exec.c
index 54cd70a..439b128 100644
--- a/exec.c
+++ b/exec.c
@@ -860,7 +860,7 @@ static RAMBlock *qemu_get_ram_block(ram_addr_t addr)
block = atomic_rcu_read(&ram_list.mru_block);
if (block && addr - block->offset < block->max_length) {
- goto found;
+ return block;
}
QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
if (addr - block->offset < block->max_length) {
--
2.5.0
next reply other threads:[~2015-10-22 11:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-22 11:51 Paolo Bonzini [this message]
2015-11-03 12:34 ` [Qemu-devel] [PATCH] exec: avoid unnecessary cacheline bounce on ram_list.mru_block Michael Tokarev
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