linux-kernel - [PATCH] x86, UV: Read RTC using replicated cachelines

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Message-ID: <20100114183422.GA12152@sgi.com>
Date:	Thu, 14 Jan 2010 12:34:22 -0600
From:	Dimitri Sivanich <sivanich@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jack Steiner <steiner@....com>, "H. Peter Anvin" <hpa@...or.com>,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: [PATCH] x86, UV: Read RTC using 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@....com>

---

Patch requires "Add function retrieving node controller revision number" patch.

 arch/x86/kernel/uv_time.c |   13 ++++++++++++-
 drivers/char/uv_mmtimer.c |   17 ++++++++++++-----
 2 files changed, 24 insertions(+), 6 deletions(-)

Index: linux/arch/x86/kernel/uv_time.c
===================================================================
--- linux.orig/arch/x86/kernel/uv_time.c	2010-01-14 11:52:44.000000000 -0600
+++ linux/arch/x86/kernel/uv_time.c	2010-01-14 11:56:57.000000000 -0600
@@ -282,10 +282,21 @@ static int uv_rtc_unset_timer(int cpu, i
 
 /*
  * 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: linux/drivers/char/uv_mmtimer.c
===================================================================
--- linux.orig/drivers/char/uv_mmtimer.c	2010-01-14 11:52:45.000000000 -0600
+++ linux/drivers/char/uv_mmtimer.c	2010-01-14 11:56:57.000000000 -0600
@@ -89,12 +89,19 @@ static long uv_mmtimer_ioctl(struct file
 	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;
-		else
+		if (PAGE_SIZE <= (1 << 16)) {
+			if (uv_get_min_hub_revision_id() == 1)
+				ret = 0;
+			else
+				ret = ((uv_blade_processor_id() *
+					L1_CACHE_BYTES) % PAGE_SIZE) / 8;
+		} else
 			ret = -ENOSYS;
 		break;
 
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