From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Christophe LEROY <christophe.leroy@c-s.fr>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Scott Wood <oss@buserror.net>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 3/5] powerpc/mm: Allow more than 16 low slices
Date: Fri, 19 Jan 2018 14:36:22 +0530 [thread overview]
Message-ID: <26a6d845-cf38-d8c6-5f54-a57ddb2a5a77@linux.vnet.ibm.com> (raw)
In-Reply-To: <baf3a2db-3522-8419-0eda-ef62ad13d76e@c-s.fr>
On 01/19/2018 02:29 PM, Christophe LEROY wrote:
>
>
> Le 19/01/2018 à 09:30, Aneesh Kumar K.V a écrit :
>> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>>
>>> While the implementation of the "slices" address space allows
>>> a significant amount of high slices, it limits the number of
>>> low slices to 16 due to the use of a single u64 low_slices_psize
>>> element in struct mm_context_t
>>>
>>> On the 8xx, the minimum slice size is the size of the area
>>> covered by a single PMD entry, ie 4M in 4K pages mode and 64M in
>>> 16K pages mode. This means we could have resp. up to 1024 and 64
>>> slices.
>>>
>>> In order to override this limitation, this patch switches the
>>> handling of low_slices to BITMAPs as done already for high_slices.
>>
>> Does it have a performance impact. When we switched high_slices
>> that was one of the question asked. Now with a topdown search we should
>> mostly be using the high_slices. But it will good to get numbers for
>> ppc64 for this change.
>
> It should have almost no performance impact at all, because all bitmap
> functions used a simplified way when the number of bits is small and
> constant:
>
> - ret->low_slices = 0;
> + slice_bitmap_zero(ret->low_slices, SLICE_NUM_LOW);
>
>
> static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
> {
> if (small_const_nbits(nbits))
> *dst = 0UL;
> else {
> unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
> memset(dst, 0, len);
> }
> }
>
>
>
> - dst->low_slices |= src->low_slices;
> + slice_bitmap_or(dst->low_slices, dst->low_slices, src->low_slices,
> + SLICE_NUM_LOW);
>
>
> static inline void bitmap_or(unsigned long *dst, const unsigned long *src1,
> const unsigned long *src2, unsigned int nbits)
> {
> if (small_const_nbits(nbits))
> *dst = *src1 | *src2;
> else
> __bitmap_or(dst, src1, src2, nbits);
> }
>
>
>
may be capture that in commit message saying since we are 64 bit on
ppc64 there is no impact there?
-aneesh
next prev parent reply other threads:[~2018-01-19 9:06 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 9:22 [PATCH v2 1/5] powerpc/mm: Enhance 'slice' for supporting PPC32 Christophe Leroy
2018-01-17 9:22 ` [PATCH v2 2/5] powerpc/32: Fix hugepage allocation on 8xx at hint address Christophe Leroy
2018-01-19 8:26 ` Aneesh Kumar K.V
2018-01-19 8:49 ` Christophe LEROY
2018-01-27 9:37 ` Michael Ellerman
2018-01-17 9:22 ` [PATCH v2 3/5] powerpc/mm: Allow more than 16 low slices Christophe Leroy
2018-01-19 8:30 ` Aneesh Kumar K.V
2018-01-19 8:59 ` Christophe LEROY
2018-01-19 9:06 ` Aneesh Kumar K.V [this message]
2018-01-17 9:22 ` [PATCH v2 4/5] powerpc/8xx: Increase the number of mm slices Christophe Leroy
2018-01-17 9:22 ` [PATCH v2 5/5] powerpc/mm: Remove intermediate bitmap copy in 'slices' Christophe Leroy
2018-01-19 8:24 ` [PATCH v2 1/5] powerpc/mm: Enhance 'slice' for supporting PPC32 Aneesh Kumar K.V
2018-01-19 8:44 ` Christophe LEROY
2018-01-19 9:02 ` Aneesh Kumar K.V
2018-01-19 9:07 ` Christophe LEROY
2018-01-19 9:13 ` Aneesh Kumar K.V
2018-01-19 9:45 ` Christophe LEROY
2018-01-20 8:22 ` christophe leroy
2018-01-20 17:56 ` Segher Boessenkool
2018-01-22 7:52 ` Christophe LEROY
2018-01-23 21:47 ` Segher Boessenkool
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