This is 2 of 3 patches for ia64 clocksource. My former patch (1 of 3) revealed that "default" has problem. It was assumed that something in combination of "fsys + jitter" is wrong since both of "nojitter (= fsys)" and "nolwsys (= non-fsys + jitter)" provides better result. Especially it is assumed as serious bug that "non-fsys + jitter", written in C is faster than "fsys + jitter", written in assembler. I picked up some points: - It seems that logics are not so different. - both uses jitter-related data in fsys_gtod_data - only fsys uses rests of contents of fsys_gtod_data, while non-fsys still uses xtime. - xtime_lock is larger lock than gtod_lock. So summary was: "reading one structure with small lock" is slower than "reading two structure with large lock" I came near to give up, but for some reason, an inspiration hit me, and at last I caught a line. > } __attribute__ ((aligned (L1_CACHE_BYTES))); The imagined situation is that a read from fsys_gtod_data was disturbed by concurrent cmpxchg of itc_lastcycle, which located in same cacheline. If so, it can be explained that why read from xtime is faster than read from fsys_gtod_data. So I made this patch to: - separate itc_lastcycle from fsys_gtod_data and put it on other cacheline. - separate itc_jitter from fsys_gtod_data too. in fact, itc_lastcycle and itc_jitter are used from both of fsys and non-fsys. Fortunately this patch works well, then the results: > # savextime : default > CPU 0: 5.49 (usecs) (0 errors / 1822461 iterations) > CPU 1: 5.46 (usecs) (0 errors / 1830527 iterations) > CPU 2: 5.45 (usecs) (0 errors / 1834697 iterations) > CPU 3: 5.46 (usecs) (0 errors / 1831464 iterations) > # savextime : nojitter > CPU 0: 0.14 (usecs) (0 errors / 70918167 iterations) > CPU 1: 0.14 (usecs) (0 errors / 71620242 iterations) > CPU 2: 0.14 (usecs) (0 errors / 70946394 iterations) > CPU 3: 0.14 (usecs) (0 errors / 70933043 iterations) > # savextime : nolwsys > CPU 0: 2.89 (usecs) (0 errors / 3459498 iterations) > CPU 1: 2.89 (usecs) (0 errors / 3458876 iterations) > CPU 2: 2.96 (usecs) (0 errors / 3377799 iterations) > CPU 3: 2.97 (usecs) (0 errors / 3372353 iterations) become more reasonable, expected level: > # separatejitter : default > CPU 0: 1.50 (usecs) (0 errors / 6677159 iterations) > CPU 1: 1.49 (usecs) (0 errors / 6697159 iterations) > CPU 2: 1.50 (usecs) (0 errors / 6664672 iterations) > CPU 3: 1.50 (usecs) (0 errors / 6668999 iterations) > # separatejitter : nojitter > CPU 0: 0.14 (usecs) (0 errors / 70580221 iterations) > CPU 1: 0.14 (usecs) (0 errors / 71275618 iterations) > CPU 2: 0.14 (usecs) (0 errors / 70626121 iterations) > CPU 3: 0.14 (usecs) (0 errors / 70603364 iterations) > # separatejitter : nolwsys > CPU 0: 2.26 (usecs) (0 errors / 4417197 iterations) > CPU 1: 2.26 (usecs) (0 errors / 4415829 iterations) > CPU 2: 2.27 (usecs) (0 errors / 4402768 iterations) > CPU 3: 2.27 (usecs) (0 errors / 4406101 iterations) (Continue to next patch.) Thanks, H.Seto Signed-off-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx> ----- arch/ia64/kernel/asm-offsets.c | 6 +++--- arch/ia64/kernel/fsys.S | 7 +++++-- arch/ia64/kernel/fsyscall_gtod_data.h | 5 ++++- arch/ia64/kernel/time.c | 12 +++++++----- 4 files changed, 19 insertions(+), 11 deletions(-) Index: linux-2.6.22/arch/ia64/kernel/asm-offsets.c =================================================================== --- linux-2.6.22.orig/arch/ia64/kernel/asm-offsets.c +++ linux-2.6.22/arch/ia64/kernel/asm-offsets.c @@ -274,8 +274,8 @@ offsetof (struct fsyscall_gtod_data_t, clk_fsys_mmio)); DEFINE(IA64_CLKSRC_CYCLE_LAST_OFFSET, offsetof (struct fsyscall_gtod_data_t, clk_cycle_last)); - DEFINE(IA64_ITC_LASTCYCLE_OFFSET, - offsetof (struct fsyscall_gtod_data_t, itc_lastcycle)); DEFINE(IA64_ITC_JITTER_OFFSET, - offsetof (struct fsyscall_gtod_data_t, itc_jitter)); + offsetof (struct itc_jitter_data_t, itc_jitter)); + DEFINE(IA64_ITC_LASTCYCLE_OFFSET, + offsetof (struct itc_jitter_data_t, itc_lastcycle)); } Index: linux-2.6.22/arch/ia64/kernel/fsys.S =================================================================== --- linux-2.6.22.orig/arch/ia64/kernel/fsys.S +++ linux-2.6.22/arch/ia64/kernel/fsys.S @@ -150,6 +150,9 @@ #if IA64_GTOD_LOCK_OFFSET !=0 #error fsys_gettimeofday incompatible with changes to struct fsyscall_gtod_data_t #endif +#if IA64_ITC_JITTER_OFFSET !=0 +#error fsys_gettimeofday incompatible with changes to struct itc_jitter_data_t +#endif #define CLOCK_REALTIME 0 #define CLOCK_MONOTONIC 1 #define CLOCK_DIVIDE_BY_1000 0x4000 @@ -215,13 +218,13 @@ add r2 = TI_FLAGS+IA64_TASK_SIZE,r16 movl r20 = fsyscall_gtod_data // load fsyscall gettimeofday data address ;; - add r29 = IA64_ITC_JITTER_OFFSET,r20 + movl r29 = itc_jitter_data // itc_jitter add r22 = IA64_GTOD_WALL_TIME_OFFSET,r20 // wall_time ld4 r2 = [r2] // process work pending flags ;; (p15) add r22 = IA64_GTOD_MONO_TIME_OFFSET,r20 // monotonic_time add r21 = IA64_CLKSRC_MMIO_OFFSET,r20 - add r19 = IA64_ITC_LASTCYCLE_OFFSET,r20 + add r19 = IA64_ITC_LASTCYCLE_OFFSET,r29 and r2 = TIF_ALLWORK_MASK,r2 (p6) br.cond.spnt.few .fail_einval // ? deferred branch ;; Index: linux-2.6.22/arch/ia64/kernel/fsyscall_gtod_data.h =================================================================== --- linux-2.6.22.orig/arch/ia64/kernel/fsyscall_gtod_data.h +++ linux-2.6.22/arch/ia64/kernel/fsyscall_gtod_data.h @@ -14,7 +14,10 @@ u32 clk_shift; void *clk_fsys_mmio; cycle_t clk_cycle_last; - cycle_t itc_lastcycle; +} __attribute__ ((aligned (L1_CACHE_BYTES))); + +struct itc_jitter_data_t { int itc_jitter; + cycle_t itc_lastcycle; } __attribute__ ((aligned (L1_CACHE_BYTES))); Index: linux-2.6.22/arch/ia64/kernel/time.c =================================================================== --- linux-2.6.22.orig/arch/ia64/kernel/time.c +++ linux-2.6.22/arch/ia64/kernel/time.c @@ -37,6 +37,8 @@ .lock = SEQLOCK_UNLOCKED, }; +struct itc_jitter_data_t itc_jitter_data; + volatile int time_keeper_id = 0; /* smp_processor_id() of time-keeper */ #ifdef CONFIG_IA64_DEBUG_IRQ @@ -236,7 +238,7 @@ * are too large. */ if (!nojitter) - fsyscall_gtod_data.itc_jitter = 1; + itc_jitter_data.itc_jitter = 1; #endif } @@ -258,10 +260,10 @@ u64 lcycle; u64 now; - if (!fsyscall_gtod_data.itc_jitter) + if (!itc_jitter_data.itc_jitter) return get_cycles(); do { - lcycle = fsyscall_gtod_data.itc_lastcycle; + lcycle = itc_jitter_data.itc_lastcycle; now = get_cycles(); if (lcycle && time_after(lcycle, now)) return lcycle; @@ -271,14 +273,14 @@ * force to retry until the write lock is released. */ if (spin_is_locked(&xtime_lock.lock)) { - fsyscall_gtod_data.itc_lastcycle = now; + itc_jitter_data.itc_lastcycle = now; return now; } /* Keep track of the last timer value returned. * The use of cmpxchg here will cause contention in * an SMP environment. */ - } while (likely(cmpxchg(&fsyscall_gtod_data.itc_lastcycle, + } while (likely(cmpxchg(&itc_jitter_data.itc_lastcycle, lcycle, now) != lcycle)); return now; } - 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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