From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks Date: Wed, 13 Jan 2016 00:10:10 +0200 Message-ID: <1452635935-5439-1-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: linux-kernel@vger.kernel.org, Linus Torvalds Cc: Davidlohr Bueso , Davidlohr Bueso , Peter Zijlstra , the arch/x86 maintainers , virtualization , "H. Peter Anvin" , Thomas Gleixner , "Paul E. McKenney" , Ingo Molnar List-Id: virtualization@lists.linuxfoundation.org mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs. So let's use the locked variant everywhere - helps keep the code simple as well. While I was at it, I found some inconsistencies in comments in arch/x86/include/asm/barrier.h I hope I'm not splitting this up too much - the reason is I wanted to isolate the code changes (that people might want to test for performance) from comment changes approved by Linus, from (so far unreviewed) comment change I came up with myself. Lightly tested on my system. Michael S. Tsirkin (3): x86: drop mfence in favor of lock+addl x86: drop a comment left over from X86_OOSTORE x86: tweak the comment about use of wmb for IO arch/x86/include/asm/barrier.h | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) -- MST