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

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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>
This commit is contained in:
Dimitri Sivanich 2010-01-22 09:41:40 -06:00 committed by Ingo Molnar
parent e0b5f80dd4
commit aca3bb5910
2 changed files with 23 additions and 8 deletions
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13
arch/x86/kernel/uv_time.c
View file

@ -282,10 +282,21 @@ static int uv_rtc_unset_timer(int cpu, int force)
/* /*
* Read the RTC. * 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) 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);
} }
/* /*

18
drivers/char/uv_mmtimer.c
View file

@ -89,13 +89,17 @@ static long uv_mmtimer_ioctl(struct file *file, unsigned int cmd,
switch (cmd) { switch (cmd) {
case MMTIMER_GETOFFSET: /* offset of the counter */ 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)) if (uv_get_min_hub_revision_id() == 1)
ret = ((UV_LOCAL_MMR_BASE | UVH_RTC) & (PAGE_SIZE-1)) ret = 0;
/ 8;
else else
ret = -ENOSYS; ret = ((uv_blade_processor_id() * L1_CACHE_BYTES) %
PAGE_SIZE) / 8;
break; break;
case MMTIMER_GETRES: /* resolution of the clock in 10^-15 s */ 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); ret = hweight64(UVH_RTC_REAL_TIME_CLOCK_MASK);
break; break;
case MMTIMER_MMAPAVAIL: /* can we mmap the clock into userspace? */ case MMTIMER_MMAPAVAIL:
ret = (PAGE_SIZE <= (1 << 16)) ? 1 : 0; ret = 1;
break; break;
case MMTIMER_GETCOUNTER: case MMTIMER_GETCOUNTER: