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Commit aca3bb59 authored by Dimitri Sivanich's avatar Dimitri Sivanich Committed by Ingo Molnar
Browse files

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: default avatarDimitri Sivanich <sivanich@sgi.com>
Cc: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20100122154140.GB4975@sgi.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e0b5f80d

arch/x86/kernel/uv_time.c

+12 −1
Original line number Diff line number Diff line
@@ -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);

}



/*

drivers/char/uv_mmtimer.c

+11 −7
Original line number Diff line number Diff line
@@ -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: