From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger-Tang Date: Tue, 31 Jan 2006 17:44:51 +0000 Subject: Re: [patch 3/6] prefetch bottom of kernel rbs stack at syscall exit path Message-Id: List-Id: References: <200601310913.k0V9DWg13193@unix-os.sc.intel.com> In-Reply-To: <200601310913.k0V9DWg13193@unix-os.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org How much latency does this add for a minimal syscall when everything is cached? --david On 1/31/06, Chen, Kenneth W wrote: > Kernel knows where the register backing store is corresponding > to user dirty stack registers. Prefetch those cache lines as > early as possible in ia64_leave_syscall path. > > Signed-off-by: Ken Chen > > > --- ./arch/ia64/kernel/entry.S.orig 2006-01-02 19:21:10.000000000 -0800 > +++ ./arch/ia64/kernel/entry.S 2006-01-30 13:26:41.161634409 -0800 > @@ -715,10 +715,11 @@ ENTRY(ia64_leave_syscall) > ;; > (p6) ld4 r31=[r18] // load current_thread_info()->flags > ld8 r19=[r2],PT(B6)-PT(LOADRS) // load ar.rsc value for "loadrs" > - nop.i 0 > + add r17=IA64_RBS_OFFSET,r13 > ;; > mov r16=ar.bsp // M2 get existing backing store pointer > ld8 r18=[r2],PT(R9)-PT(B6) // load b6 > + shr r22=r19,16 > (p6) and r15=TIF_WORK_MASK,r31 // any work other than TIF_SYSCALL_TRACE? > ;; > ld8 r23=[r3],PT(R11)-PT(AR_BSPSTORE) // load ar.bspstore (may be garbage) > @@ -729,6 +730,12 @@ ENTRY(ia64_leave_syscall) > ld8 r9=[r2],PT(CR_IPSR)-PT(R9) > ld8 r11=[r3],PT(CR_IIP)-PT(R11) > (pNonSys) break 0 // bug check: we shouldn't be here if pNonSys is TRUE! > +1: > +(pUStk) lfetch [r17],128 > + add r22=-128,r22 > + ;; > +(pUStk) cmp.gt.unc p7,p0=r22,r0 > +(p7) br.dptk.few 1b > ;; > invala // M0|1 invalidate ALAT > rsm psr.i | psr.ic // M2 turn off interrupts and interruption collection > > > - > To unsubscribe from this list: send the line "unsubscribe linux-ia64" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Mosberger Consulting LLC, http://www.mosberger-consulting.com/