Messages in this thread | | | Date | Wed, 20 Jan 2010 09:10:20 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86, UV: Fix RTC latency bug by reading replicated cachelines |
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* Dimitri Sivanich <sivanich@sgi.com> wrote:
> +++ 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
That 64K PAGE_SIZE check in the ioctl looks rather weird. What is the purpose of it?
Ingo
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