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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
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@@ -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);
}
/*