From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: [PATCH] x86/current: Provide additional information to optimise get_cpu_info() Date: Mon, 1 Sep 2014 11:58:50 +0100 Message-ID: <1409569130-19066-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Xen-devel Cc: Andrew Cooper , Jan Beulich List-Id: xen-devel@lists.xenproject.org Exactly as with c/s d55c5eefe "x86: use compiler visible "add" instead of inline assembly "or" in get_cpu_info()", this is achieved by providing more information to the compiler. With this modification, gcc replaces the older: mov imm, %reg and %rsp, %reg with: mov %rsp, %reg and imm, %reg which is one byte shorter. It also considers all general purpose registers for %reg rather than just the legacy ones (i.e. will now use %r12 etc), which allows for better register scheduling in larger functions. This causes a net drop of almost 4K of .text Signed-off-by: Andrew Cooper CC: Jan Beulich --- xen/include/asm-x86/current.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/xen/include/asm-x86/current.h b/xen/include/asm-x86/current.h index 2081015..b95fd79 100644 --- a/xen/include/asm-x86/current.h +++ b/xen/include/asm-x86/current.h @@ -25,9 +25,9 @@ struct cpu_info { static inline struct cpu_info *get_cpu_info(void) { - unsigned long tos; - __asm__ ( "and %%rsp,%0" : "=r" (tos) : "0" (~(STACK_SIZE-1)) ); - return (struct cpu_info *)(tos + STACK_SIZE) - 1; + register unsigned long sp asm("rsp"); + + return (struct cpu_info *)((sp & ~(STACK_SIZE-1)) + STACK_SIZE) - 1; } #define get_current() (get_cpu_info()->current_vcpu) -- 1.7.10.4