From: Yicong Yang <yangyicong@huawei.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
<akpm@linux-foundation.org>, <linux-mm@kvack.org>,
<linux-arm-kernel@lists.infradead.org>, <x86@kernel.org>,
<catalin.marinas@arm.com>, <will@kernel.org>,
<linux-doc@vger.kernel.org>
Cc: wangkefeng.wang@huawei.com, darren@os.amperecomputing.com,
peterz@infradead.org, yangyicong@hisilicon.com,
punit.agrawal@bytedance.com, Nadav Amit <namit@vmware.com>,
guojian@oppo.com, linux-riscv@lists.infradead.org,
linux-s390@vger.kernel.org, zhangshiming@oppo.com,
lipeifeng@oppo.com, corbet@lwn.net,
Barry Song <21cnbao@gmail.com>, Mel Gorman <mgorman@suse.de>,
linux-mips@vger.kernel.org, arnd@arndb.de, realmz6@gmail.com,
Barry Song <v-songbaohua@oppo.com>,
openrisc@lists.librecores.org, prime.zeng@hisilicon.com,
xhao@linux.alibaba.com, linux-kernel@vger.kernel.org,
huzhanyuan@oppo.com, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v5 2/2] arm64: support batched/deferred tlb shootdown during page reclamation
Date: Tue, 15 Nov 2022 11:34:44 +0800 [thread overview]
Message-ID: <5bbd5364-fcec-5fc2-4780-e9b44f2ab135@huawei.com> (raw)
In-Reply-To: <40f1b5ad-2165-bb81-1ff5-89786373fa14@arm.com>
On 2022/11/14 22:19, Anshuman Khandual wrote:
>
>
> On 11/14/22 14:16, Yicong Yang wrote:
>> On 2022/11/14 11:29, Anshuman Khandual wrote:
>>>
>>> On 10/28/22 13:42, Yicong Yang wrote:
>>>> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
>>>> +{
>>>> + /*
>>>> + * TLB batched flush is proved to be beneficial for systems with large
>>>> + * number of CPUs, especially system with more than 8 CPUs. TLB shutdown
>>>> + * is cheap on small systems which may not need this feature. So use
>>>> + * a threshold for enabling this to avoid potential side effects on
>>>> + * these platforms.
>>>> + */
>>>> + if (num_online_cpus() <= CONFIG_ARM64_NR_CPUS_FOR_BATCHED_TLB)
>>>> + return false;
>>>> +
>>>> +#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI
>>>> + if (unlikely(this_cpu_has_cap(ARM64_WORKAROUND_REPEAT_TLBI)))
>>>> + return false;
>>>> +#endif
>>> should_defer_flush() is immediately followed by set_tlb_ubc_flush_pending() which calls
>>> arch_tlbbatch_add_mm(), triggering the actual TLBI flush via __flush_tlb_page_nosync().
>>> It should be okay to check capability with this_cpu_has_cap() as the entire call chain
>>> here is executed on the same cpu. But just wondering if cpus_have_const_cap() would be
>>> simpler, consistent, and also cost effective ?
>>>
>> ok. Checked cpus_have_const_cap() I think it matches your words.
>>
>>> Regardless, a comment is needed before the #ifdef block explaining why it does not make
>>> sense to defer/batch when __tlbi()/__tlbi_user() implementation will execute 'dsb(ish)'
>>> between two TLBI instructions to workaround the errata.
>>>
>> The workaround for the errata mentioned the affected platforms need the tlbi+dsb to be done
>> twice, so I'm not sure if we defer the final dsb will cause any problem so I think the judgement
>> here is used for safety. I have no such platform to test if it's ok to defer the last dsb.
>
> We should not defer TLB flush on such systems, as ensured by the above test and 'false'
> return afterwards. The only question is whether this decision should be taken at a CPU
> level (which is affected by the errata) or the whole system level.
>
> What is required now
>
> - Replace this_cpu_has_cap() with cpus_have_const_cap ?
> - Add the following comment before the #ifdef check
>
Have respin the series according to the above comments:
https://lore.kernel.org/lkml/20221115031425.44640-3-yangyicong@huawei.com/
Thanks.
> /*
> * TLB flush deferral is not required on systems, which are affected with
> * ARM64_WORKAROUND_REPEAT_TLBI, as __tlbi()/__tlbi_user() implementation
> * will have two consecutive TLBI instructions with a dsb(ish) in between
> * defeating the purpose (i.e save overall 'dsb ish' cost).
> */
>
> .
>
next prev parent reply other threads:[~2022-11-15 3:34 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-28 8:12 [PATCH v5 0/2] arm64: support batched/deferred tlb shootdown during page reclamation Yicong Yang
2022-10-28 8:12 ` [PATCH v5 1/2] mm/tlbbatch: Introduce arch_tlbbatch_should_defer() Yicong Yang
2022-10-28 8:12 ` [PATCH v5 2/2] arm64: support batched/deferred tlb shootdown during page reclamation Yicong Yang
2022-11-14 3:29 ` Anshuman Khandual
2022-11-14 8:46 ` Yicong Yang
2022-11-14 14:19 ` Anshuman Khandual
2022-11-15 3:34 ` Yicong Yang [this message]
2022-11-14 8:00 ` haoxin
2022-11-11 10:17 ` [External] [PATCH v5 0/2] " Punit Agrawal
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5bbd5364-fcec-5fc2-4780-e9b44f2ab135@huawei.com \
--to=yangyicong@huawei.com \
--cc=21cnbao@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=anshuman.khandual@arm.com \
--cc=arnd@arndb.de \
--cc=catalin.marinas@arm.com \
--cc=corbet@lwn.net \
--cc=darren@os.amperecomputing.com \
--cc=guojian@oppo.com \
--cc=huzhanyuan@oppo.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-riscv@lists.infradead.org \
--cc=linux-s390@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=lipeifeng@oppo.com \
--cc=mgorman@suse.de \
--cc=namit@vmware.com \
--cc=openrisc@lists.librecores.org \
--cc=peterz@infradead.org \
--cc=prime.zeng@hisilicon.com \
--cc=punit.agrawal@bytedance.com \
--cc=realmz6@gmail.com \
--cc=v-songbaohua@oppo.com \
--cc=wangkefeng.wang@huawei.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
--cc=xhao@linux.alibaba.com \
--cc=yangyicong@hisilicon.com \
--cc=zhangshiming@oppo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).