From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 22 Oct 2015 11:51:30 +0000 (+0200)
Subject: exec: avoid unnecessary cacheline bounce on ram_list.mru_block
X-Git-Url: https://repo.jachan.dev/qemu.git/commitdiff_plain/68851b98e5bf6d397498b74f1776801274ab8d48

exec: avoid unnecessary cacheline bounce on ram_list.mru_block

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>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---

diff --git a/exec.c b/exec.c
index ed88e72f14..a028961587 100644
--- a/exec.c
+++ b/exec.c
@@ -903,7 +903,7 @@ 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) {