From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Zhenyu Ye <yezhenyu2@huawei.com>,
mark.rutland@arm.com, will@kernel.org, catalin.marinas@arm.com,
aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org,
npiggin@gmail.com, arnd@arndb.de, maz@kernel.org,
suzuki.poulose@arm.com, tglx@linutronix.de, yuzhao@google.com,
Dave.Martin@arm.com, steven.price@arm.com, broonie@kernel.org,
guohanjun@huawei.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
linux-mm@kvack.org, arm@kernel.org, xiexiangyou@huawei.com,
prime.zeng@hisilicon.com, zhangshaokun@hisilicon.com,
kuhn.chenqun@huawei.com
Subject: Re: [PATCH v1 6/6] arm64: tlb: Set the TTL field in flush_tlb_range
Date: Tue, 21 Apr 2020 10:30:43 +0200 [thread overview]
Message-ID: <20200421083043.GP20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200420200616.44c7c7ea@oasis.local.home>
On Mon, Apr 20, 2020 at 08:06:16PM -0400, Steven Rostedt wrote:
> Peter Zijlstra <peterz@infradead.org> wrote:
> > On Fri, Apr 03, 2020 at 05:00:48PM +0800, Zhenyu Ye wrote:
> > > +static inline int tlb_get_level(struct mmu_gather *tlb)
> > > +{
> > > + int sum = tlb->cleared_ptes + tlb->cleared_pmds +
> > > + tlb->cleared_puds + tlb->cleared_p4ds;
> > > +
> > > + if (sum != 1)
> > > + return 0;
> > > + else if (tlb->cleared_ptes)
> > > + return 3;
> > > + else if (tlb->cleared_pmds)
> > > + return 2;
> > > + else if (tlb->cleared_puds)
> > > + return 1;
> > > +
> > > + return 0;
> > > +}
> >
> > That's some mighty wonky code. Please look at the generated asm.
>
> Without even looking at the generated asm, if a condition returns,
> there's no reason to add an else for that condition.
Not really the point; he wants to guarantee he only returns >0 when
there's a single bit set. But the thing is, cleared_* is a bitfield, and
I'm afraid that the above will result in some terrible code-gen.
Maybe something like:
if (tlb->cleared_ptes && !(tlb->cleared_pmds ||
tlb->cleared_puds ||
tlb->cleared_p4ds))
return 3;
if (tlb->cleared_pmds && !(tlb->cleared_ptes ||
tlb->cleared_puds ||
tlb->cleared_p4ds))
return 2;
if (tlb->cleared_puds && !(tlb->cleared_ptes ||
tlb->cleared_pmds ||
tlb->cleared_p4ds))
return 1;
return 0;
Which I admit is far too much typing, but I suspect it generates far
saner code (just a few masks and branches).
But maybe the compiler surprises us, what do I konw.
next prev parent reply other threads:[~2020-04-21 8:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-03 9:00 [PATCH v1 0/6] arm64: tlb: add support for TTL feature Zhenyu Ye
2020-04-03 9:00 ` [PATCH v1 1/6] arm64: Detect the ARMv8.4 " Zhenyu Ye
2020-04-21 16:53 ` Christoph Hellwig
2020-04-21 17:13 ` Peter Zijlstra
2020-04-21 17:16 ` Christoph Hellwig
2020-04-22 2:13 ` Zhenyu Ye
2020-04-03 9:00 ` [PATCH v1 2/6] arm64: Add level-hinted TLB invalidation helper Zhenyu Ye
2020-04-03 9:00 ` [PATCH v1 3/6] arm64: Add tlbi_user_level " Zhenyu Ye
2020-04-03 9:00 ` [PATCH v1 4/6] tlb: mmu_gather: add tlb_set_*_range APIs Zhenyu Ye
2020-04-20 11:46 ` Peter Zijlstra
2020-04-03 9:00 ` [PATCH v1 5/6] mm: tlb: Provide flush_*_tlb_range wrappers Zhenyu Ye
2020-04-20 12:09 ` Peter Zijlstra
2020-04-21 14:18 ` Zhenyu Ye
2020-04-03 9:00 ` [PATCH v1 6/6] arm64: tlb: Set the TTL field in flush_tlb_range Zhenyu Ye
2020-04-20 12:10 ` Peter Zijlstra
2020-04-21 0:06 ` Steven Rostedt
2020-04-21 8:30 ` Peter Zijlstra [this message]
2020-04-21 12:22 ` Zhenyu Ye
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=20200421083043.GP20730@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=Dave.Martin@arm.com \
--cc=akpm@linux-foundation.org \
--cc=aneesh.kumar@linux.ibm.com \
--cc=arm@kernel.org \
--cc=arnd@arndb.de \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=guohanjun@huawei.com \
--cc=kuhn.chenqun@huawei.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mark.rutland@arm.com \
--cc=maz@kernel.org \
--cc=npiggin@gmail.com \
--cc=prime.zeng@hisilicon.com \
--cc=rostedt@goodmis.org \
--cc=steven.price@arm.com \
--cc=suzuki.poulose@arm.com \
--cc=tglx@linutronix.de \
--cc=will@kernel.org \
--cc=xiexiangyou@huawei.com \
--cc=yezhenyu2@huawei.com \
--cc=yuzhao@google.com \
--cc=zhangshaokun@hisilicon.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 NNTP newsgroup(s).