x86, UV: Fix RTC latency bug by reading replicated cachelines
Dimitri Sivanich [Fri, 22 Jan 2010 15:41:40 +0000 (09:41 -0600)]
For SGI UV node controllers (HUB) rev 2.0 or greater, use
replicated cachelines to read the RTC timer.  This optimization
allows faster simulataneous reads from a given socket.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Cc: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20100122154140.GB4975@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/uv_time.c
drivers/char/uv_mmtimer.c

index 3c84aa0..2b75ef6 100644 (file)
@@ -282,10 +282,21 @@ static int uv_rtc_unset_timer(int cpu, int force)
 
 /*
  * Read the RTC.
+ *
+ * Starting with HUB rev 2.0, the UV RTC register is replicated across all
+ * cachelines of it's own page.  This allows faster simultaneous reads
+ * from a given socket.
  */
 static cycle_t uv_read_rtc(struct clocksource *cs)
 {
-       return (cycle_t)uv_read_local_mmr(UVH_RTC);
+       unsigned long offset;
+
+       if (uv_get_min_hub_revision_id() == 1)
+               offset = 0;
+       else
+               offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;
+
+       return (cycle_t)uv_read_local_mmr(UVH_RTC | offset);
 }
 
 /*
index 867b67b..c7072ba 100644 (file)
@@ -89,13 +89,17 @@ static long uv_mmtimer_ioctl(struct file *file, unsigned int cmd,
        switch (cmd) {
        case MMTIMER_GETOFFSET: /* offset of the counter */
                /*
-                * UV RTC register is on its own page
+                * Starting with HUB rev 2.0, the UV RTC register is
+                * replicated across all cachelines of it's own page.
+                * This allows faster simultaneous reads from a given socket.
+                *
+                * The offset returned is in 64 bit units.
                 */
-               if (PAGE_SIZE <= (1 << 16))
-                       ret = ((UV_LOCAL_MMR_BASE | UVH_RTC) & (PAGE_SIZE-1))
-                               / 8;
+               if (uv_get_min_hub_revision_id() == 1)
+                       ret = 0;
                else
-                       ret = -ENOSYS;
+                       ret = ((uv_blade_processor_id() * L1_CACHE_BYTES) %
+                                       PAGE_SIZE) / 8;
                break;
 
        case MMTIMER_GETRES: /* resolution of the clock in 10^-15 s */
@@ -115,8 +119,8 @@ static long uv_mmtimer_ioctl(struct file *file, unsigned int cmd,
                ret = hweight64(UVH_RTC_REAL_TIME_CLOCK_MASK);
                break;
 
-       case MMTIMER_MMAPAVAIL: /* can we mmap the clock into userspace? */
-               ret = (PAGE_SIZE <= (1 << 16)) ? 1 : 0;
+       case MMTIMER_MMAPAVAIL:
+               ret = 1;
                break;
 
        case MMTIMER_GETCOUNTER: