From: Gautham R Shenoy <ego@linux•vnet.ibm.com>
To: Nicholas Piggin <npiggin@gmail•com>
Cc: linuxppc-dev@lists•ozlabs.org,
Michael Ellerman <mpe@ellerman•id.au>,
"Gautham R . Shenoy" <ego@linux•vnet.ibm.com>,
Mahesh Jagannath Salgaonkar <mahesh@linux•vnet.ibm.com>
Subject: Re: [PATCH 7/7] powerpc/64s: idle POWER8 avoid full state loss recovery where possible
Date: Mon, 20 Mar 2017 15:41:39 +0530 [thread overview]
Message-ID: <20170320101139.GA20417@in.ibm.com> (raw)
In-Reply-To: <20170320060152.1016-8-npiggin@gmail.com>
Hi Nick,
On Mon, Mar 20, 2017 at 04:01:52PM +1000, Nicholas Piggin wrote:
> If not all threads were in winkle, full state loss recovery is not
> necessary and can be avoided. A previous patch removed this optimisation
> due to some complexity with the implementation. Re-implement it by
> counting the number of threads in winkle with the per-core idle state.
> Only restore full state loss if all threads were in winkle.
>
> This has a small window of false positives right before threads execute
> winkle and just after they wake up, when the winkle count does not
> reflect the true number of threads in winkle. This is not a significant
> problem in comparison with even the minimum winkle duration. For
> correctness, a false positive is not a problem (only false negatives
> would be).
The patch looks good. Just a minor comment.
> BEGIN_FTR_SECTION
> + /*
> + * Were we in winkle?
> + * If yes, check if all threads were in winkle, decrement our
> + * winkle count, set all thread winkle bits if all were in winkle.
> + * Check if our thread has a winkle bit set, and set cr4 accordingly
> + * (to match ISA300, above). Pseudo-code for core idle state
> + * transitions for ISA207 is as follows (everything happens atomically
> + * due to store conditional and/or lock bit):
> + *
> + * nap_idle() { }
> + * nap_wake() { }
> + *
> + * sleep_idle()
> + * {
> + * core_idle_state &= ~thread_in_core
> + * }
> + *
> + * sleep_wake()
> + * {
> + * bool first_in_core, first_in_subcore;
> + *
> + * first_in_core = (core_idle_state & IDLE_THREAD_BITS) == 0;
> + * first_in_subcore = (core_idle_state & SUBCORE_SIBLING_MASK) == 0;
> + *
> + * core_idle_state |= thread_in_core;
> + * }
> + *
> + * winkle_idle()
> + * {
> + * core_idle_state &= ~thread_in_core;
> + * core_idle_state += 1 << WINKLE_COUNT_SHIFT;
> + * }
> + *
> + * winkle_wake()
> + * {
> + * bool first_in_core, first_in_subcore, winkle_state_lost;
> + *
> + * first_in_core = (core_idle_state & IDLE_THREAD_BITS) == 0;
> + * first_in_subcore = (core_idle_state & SUBCORE_SIBLING_MASK) == 0;
> + *
> + * core_idle_state |= thread_in_core;
> + *
> + * if ((core_idle_state & WINKLE_MASK) == (8 << WINKLE_COUNT_SIHFT))
> + * core_idle_state |= THREAD_WINKLE_BITS;
We also do the following decrement. I forgot this in the pseudo-code in my
earlier reply.
core_idle_state -= 1 << WINKLE_COUNT_SHIFT;
> + * winkle_state_lost = core_idle_state &
> + * (thread_in_core << WINKLE_THREAD_SHIFT);
> + * core_idle_state &= ~(thread_in_core << WINKLE_THREAD_SHIFT);
> + * }
> + *
> + */
> + cmpwi r18,PNV_THREAD_WINKLE
> + bne 2f
> + andis. r9,r15,PNV_CORE_IDLE_WINKLE_COUNT_ALL_BIT@h
> + subis r15,r15,PNV_CORE_IDLE_WINKLE_COUNT@h
> + beq 2f
> + ori r15,r15,PNV_CORE_IDLE_THREAD_WINKLE_BITS /* all were winkle */
> +2:
> + /* Shift thread bit to winkle mask, then test if this thread is set,
> + * and remove it from the winkle bits */
> + slwi r8,r7,8
> + and r8,r8,r15
> + andc r15,r15,r8
> + cmpwi cr4,r8,1 /* cr4 will be gt if our bit is set, lt if not */
> +
Looks good other wise.
Reviewed-by: Gautham R. Shenoy <ego@linux•vnet.ibm.com>
> lbz r4,PACA_SUBCORE_SIBLING_MASK(r13)
> and r4,r4,r15
> cmpwi r4,0 /* Check if first in subcore */
> --
> 2.11.0
>
next prev parent reply other threads:[~2017-03-20 10:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-20 6:01 [PATCH 0/7][v3] idle fixes and changes for POWER8 and POWER9 Nicholas Piggin
2017-03-20 6:01 ` [PATCH 1/7] powerpc/64s: move remaining system reset idle code into idle_book3s.S Nicholas Piggin
2017-03-20 6:01 ` [PATCH 2/7] powerpc/64s: stop using bit in HSPRG0 to test winkle Nicholas Piggin
2017-03-20 6:01 ` [PATCH 3/7] powerpc/64s: use alternative feature patching Nicholas Piggin
2017-03-20 6:01 ` [PATCH 4/7] powerpc/64s: fix POWER9 machine check handler from stop state Nicholas Piggin
2017-03-20 14:51 ` Nicholas Piggin
2017-03-20 6:01 ` [PATCH 5/7] powerpc/64s: idle expand core idle state bits Nicholas Piggin
2017-03-20 6:01 ` [PATCH 6/7] powerpc/64s: idle do not hold reservation longer than required Nicholas Piggin
2017-03-20 6:01 ` [PATCH 7/7] powerpc/64s: idle POWER8 avoid full state loss recovery where possible Nicholas Piggin
2017-03-20 10:11 ` Gautham R Shenoy [this message]
2017-03-20 10:26 ` Nicholas Piggin
2017-03-20 16:31 ` Gautham R Shenoy
2017-03-20 17:19 ` Nicholas Piggin
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