Messages in this thread Patch in this message | | | Date | Tue, 19 Jan 2010 08:41:37 -0600 | From | Dimitri Sivanich <> | Subject | [PATCH] x86, UV: Fix RTC latency bug by reading replicated cachelines |
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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 <sivanich@sgi.com>
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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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