x86, UV: Fix RTC latency bug by reading replicated cachelines

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>

1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/char/uv_mmtimer.c b/drivers/char/uv_mmtimer.c
index 867b67be9f0..c7072ba14f4 100644
--- a/drivers/char/uv_mmtimer.c
+++ b/drivers/char/uv_mmtimer.c
@@ -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: