Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753738Ab0ASOll (ORCPT ); Tue, 19 Jan 2010 09:41:41 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751522Ab0ASOlk (ORCPT ); Tue, 19 Jan 2010 09:41:40 -0500 Received: from relay2.sgi.com ([192.48.179.30]:50803 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751512Ab0ASOlj (ORCPT ); Tue, 19 Jan 2010 09:41:39 -0500 Date: Tue, 19 Jan 2010 08:41:37 -0600 From: Dimitri Sivanich To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Jack Steiner , "H. Peter Anvin" , tglx@linutronix.de Subject: [PATCH] x86, UV: Fix RTC latency bug by reading replicated cachelines Message-ID: <20100119144137.GB22276@sgi.com> References: <20100112210904.GA24546@sgi.com> <20100113092433.GB6739@elte.hu> <20100114183422.GA12152@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100114183422.GA12152@sgi.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2517 Lines: 74 Fix an RTC read latency bug by using replicated cachelines to read the RTC timer on SGI UV node controllers (HUB) rev 2.0 or greater. Signed-off-by: Dimitri Sivanich --- 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/