On Mon, 2008-09-15 at 18:36 +0200, Petr Tesarik wrote: > Hello, > > I know there are currently enough TIF_ flags, but some time ago I > promised to post a patch that extends their very limited number to 8. > > The main reason for having special work-to-be-done bits is that they can > be checked by a more efficient CPU instruction. The reason for only > having 7 such bits on IA64 is that the "and" instruction sign-extends > its immediate argument. > > Since the assembler code never cares about the high bits, it is possible > to load only the first byte from the thread flags. The 8-bit value is > zero-extended, so the sign extension of the most significant bit in the > "and immediate" instruction does not matter (it gets masked off by the > register content itself). This allows to use 8 TIF_ flags for pending > work to be done. No comments? Does it mean the patch is not needed/wanted? I can recall that some time ago perfmon would have liked to have an additional TIF flag. Anyway, having 8 bits instead of 7, and that for free, sounds like an improvement to me... Or, are the 8-bit loads less efficient than 32-bit loads? Something else? Petr > > Signed-off-by: Petr Tesarik <ptesarik@xxxxxxx> > > diff --git a/arch/ia64/include/asm/thread_info.h b/arch/ia64/include/asm/thread_info.h > index 7c60fcd..e30c470 100644 > --- a/arch/ia64/include/asm/thread_info.h > +++ b/arch/ia64/include/asm/thread_info.h > @@ -95,8 +95,8 @@ extern void tsk_clear_notify_resume(struct task_struct *tsk); > /* > * thread information flags > * - these are process state flags that various assembly files may need to access > - * - pending work-to-be-done flags are in least-significant 16 bits, other flags > - * in top 16 bits > + * - pending work-to-be-done flags are in least-significant 8 bits, other flags > + * in top 24 bits > */ > #define TIF_SIGPENDING 0 /* signal pending */ > #define TIF_NEED_RESCHED 1 /* rescheduling necessary */ > diff --git a/arch/ia64/kernel/entry.S b/arch/ia64/kernel/entry.S > index 0dd6c14..3bc2119 100644 > --- a/arch/ia64/kernel/entry.S > +++ b/arch/ia64/kernel/entry.S > @@ -626,7 +626,7 @@ GLOBAL_ENTRY(ia64_ret_from_clone) > .ret8: > adds r2=TI_FLAGS+IA64_TASK_SIZE,r13 > ;; > - ld4 r2=[r2] > + ld1 r2=[r2] > ;; > mov r8=0 > and r2=_TIF_SYSCALL_TRACEAUDIT,r2 > @@ -732,7 +732,7 @@ __paravirt_work_processed_syscall: > (pUStk) mov.m r22=ar.itc // fetch time at leave > adds r18=TI_FLAGS+IA64_TASK_SIZE,r13 > ;; > -(p6) ld4 r31=[r18] // load current_thread_info()->flags > +(p6) ld1 r31=[r18] // r31 = current_thread_info()->flags & 0xff > ld8 r19=[r2],PT(B6)-PT(LOADRS) // load ar.rsc value for "loadrs" > adds r3=PT(AR_BSPSTORE)+16,r12 // deferred > ;; > @@ -741,7 +741,7 @@ __paravirt_work_processed_syscall: > adds r3=PT(AR_BSPSTORE)+16,r12 > adds r18=TI_FLAGS+IA64_TASK_SIZE,r13 > ;; > -(p6) ld4 r31=[r18] // load current_thread_info()->flags > +(p6) ld1 r31=[r18] // r31 = current_thread_info()->flags & 0xff > ld8 r19=[r2],PT(B6)-PT(LOADRS) // load ar.rsc value for "loadrs" > nop.i 0 > ;; > @@ -896,7 +896,7 @@ GLOBAL_ENTRY(__paravirt_leave_kernel) > .work_processed_kernel: > adds r17=TI_FLAGS+IA64_TASK_SIZE,r13 > ;; > -(p6) ld4 r31=[r17] // load current_thread_info()->flags > +(p6) ld1 r31=[r17] // r31 = current_thread_info()->flags & 0xff > adds r21=PT(PR)+16,r12 > ;; > > diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S > index c1625c7..d9feb9c 100644 > --- a/arch/ia64/kernel/fsys.S > +++ b/arch/ia64/kernel/fsys.S > @@ -66,7 +66,7 @@ ENTRY(fsys_getpid) > ld8 r17=[r17] // r17 = current->group_leader > add r9=TI_FLAGS+IA64_TASK_SIZE,r16 > ;; > - ld4 r9=[r9] > + ld1 r9=[r9] > add r17=IA64_TASK_TGIDLINK_OFFSET,r17 > ;; > and r9=TIF_ALLWORK_MASK,r9 > @@ -100,7 +100,7 @@ ENTRY(fsys_getppid) > add r9=TI_FLAGS+IA64_TASK_SIZE,r16 > ;; > > - ld4 r9=[r9] > + ld1 r9=[r9] > add r17=IA64_TASK_REAL_PARENT_OFFSET,r17 // r17 = ¤t->group_leader->real_parent > ;; > and r9=TIF_ALLWORK_MASK,r9 > @@ -144,7 +144,7 @@ ENTRY(fsys_set_tid_address) > add r9=TI_FLAGS+IA64_TASK_SIZE,r16 > add r17=IA64_TASK_TGIDLINK_OFFSET,r16 > ;; > - ld4 r9=[r9] > + ld1 r9=[r9] > tnat.z p6,p7=r32 // check argument register for being NaT > ld8 r17=[r17] // r17 = current->pids[PIDTYPE_PID].pid > ;; > @@ -242,7 +242,7 @@ ENTRY(fsys_gettimeofday) > (p6) br.cond.spnt.few .fail_einval > movl r20 = fsyscall_gtod_data // load fsyscall gettimeofday data address > ;; > - ld4 r2 = [r2] // process work pending flags > + ld1 r2 = [r2] // process work pending flags > movl r29 = itc_jitter_data // itc_jitter > add r22 = IA64_GTOD_WALL_TIME_OFFSET,r20 // wall_time > add r21 = IA64_CLKSRC_MMIO_OFFSET,r20 > @@ -391,7 +391,7 @@ ENTRY(fsys_rt_sigprocmask) > add r31=IA64_TASK_SIGHAND_OFFSET,r16 > ;; > ld8 r3=[r2] // read/prefetch current->blocked > - ld4 r9=[r9] > + ld1 r9=[r9] > tnat.nz.or p6,p0=r35 > > cmp.ne.or p6,p0=_NSIG_WORDS*8,r35 > @@ -476,14 +476,14 @@ EX(.fail_efault, ld8 r14=[r33]) // r14 <- *set > (p6) br.cond.dpnt.many .sig_pending > ;; > > -1: ld4 r17=[r9] // r17 <- current->thread_info->flags > +1: ld1 r17=[r9] // r17 <- current->thread_info->flags & 0xff > ;; > mov ar.ccv=r17 > and r18=~_TIF_SIGPENDING,r17 // r18 <- r17 & ~(1 << TIF_SIGPENDING) > ;; > > st8 [r2]=r14 // update current->blocked with new mask > - cmpxchg4.acq r8=[r9],r18,ar.ccv // current->thread_info->flags <- r18 > + cmpxchg1.acq r8=[r9],r18,ar.ccv // current->thread_info->flags <- r18 > ;; > cmp.ne p6,p0=r17,r8 // update failed? > (p6) br.cond.spnt.few 1b // yes -> retry > @@ -542,7 +542,7 @@ ENTRY(fsys_getcpu) > add r3=TI_CPU+IA64_TASK_SIZE,r16 > ;; > ld4 r3=[r3] // M r3 = thread_info->cpu > - ld4 r2=[r2] // M r2 = thread_info->flags > + ld1 r2=[r2] // M r2 = thread_info->flags & 0xff > (p6) br.cond.spnt.few .fail_einval // B > ;; > tnat.nz p7,p0 = r33 // I guard against NaT argument > @@ -677,7 +677,7 @@ GLOBAL_ENTRY(fsys_bubble_down) > addl r22=IA64_RBS_OFFSET,r2 // A compute base of RBS > add r3=TI_FLAGS+IA64_TASK_SIZE,r2 // A > ;; > - ld4 r3=[r3] // M0|1 r3 = current_thread_info()->flags > + ld1 r3=[r3] // M0|1 r3 = current_thread_info()->flags & 0xff > lfetch.fault.excl.nt1 [r22] // M0|1 prefetch register backing-store > nop.i 0 > ;; > diff --git a/arch/ia64/kernel/ivt.S b/arch/ia64/kernel/ivt.S > index 416a952..4ab0253 100644 > --- a/arch/ia64/kernel/ivt.S > +++ b/arch/ia64/kernel/ivt.S > @@ -765,7 +765,7 @@ ENTRY(break_fault) > mov r3=NR_syscalls - 1 > ;; > ld1.bias r17=[r16] // M0|1 r17 = current->thread.on_ustack flag > - ld4 r9=[r9] // M0|1 r9 = current_thread_info()->flags > + ld1 r9=[r9] // M0|1 r9 = current_thread_info()->flags > extr.u r8=r29,41,2 // I0 extract ei field from cr.ipsr > > shladd r30=r15,3,r30 // A r30 = sys_call_table + 8*(syscall-1024) > @@ -1775,7 +1775,7 @@ ENTRY(dispatch_to_ia32_handler) > movl r16=ia32_syscall_table > ;; > (p6) shladd r16=r8,3,r16 // force ni_syscall if not valid syscall number > - ld4 r2=[r2] // r2 = current_thread_info()->flags > + ld1 r2=[r2] // r2 = current_thread_info()->flags > ;; > ld8 r16=[r16] > and r2=_TIF_SYSCALL_TRACEAUDIT,r2 // mask trace or audit > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ia64" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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