From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: catalin.marinas@arm.com, will@kernel.org,
Ard Biesheuvel <ardb@kernel.org>,
linux-arm-kernel@lists.infradead.org, james.morse@arm.com
Subject: Re: [PATCH v2] arm64: implement support for static call trampolines
Date: Thu, 29 Oct 2020 12:58:32 +0100 [thread overview]
Message-ID: <20201029115832.GO2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201029115026.GA61831@C02TD0UTHF1T.local>
On Thu, Oct 29, 2020 at 11:50:26AM +0000, Mark Rutland wrote:
> Hi Ard,
>
> On Wed, Oct 28, 2020 at 07:41:14PM +0100, Ard Biesheuvel wrote:
> > Implement arm64 support for the 'unoptimized' static call variety,
> > which routes all calls through a single trampoline that is patched
> > to perform a tail call to the selected function.
>
> Given the complexity and subtlety here, do we actually need this?
Only if you can get a performance win. The obvious benefit is loosing
the load that's inherent in indirect function calls. The down-side of
the indirect static-call implementation is that it will incur an extra
I$ miss.
So it might be a wash, loose a data load miss, gain an I$ miss.
The direct method (patching the call-site, where possible) would
alleviate that (mostly) and be more of a win.
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next prev parent reply other threads:[~2020-10-29 12:00 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 18:41 [PATCH v2] arm64: implement support for static call trampolines Ard Biesheuvel
2020-10-29 10:28 ` Peter Zijlstra
2020-10-29 10:40 ` Peter Zijlstra
2020-10-29 10:58 ` Ard Biesheuvel
2020-10-29 11:46 ` Peter Zijlstra
2020-10-29 11:49 ` Ard Biesheuvel
2020-10-29 11:54 ` Peter Zijlstra
2020-10-29 12:14 ` Ard Biesheuvel
2020-10-29 11:27 ` Quentin Perret
2020-10-29 11:32 ` Ard Biesheuvel
2020-10-29 11:44 ` Peter Zijlstra
2020-10-29 14:10 ` Steven Rostedt
2020-10-29 11:54 ` Quentin Perret
2020-10-29 13:22 ` Ard Biesheuvel
2020-11-16 10:18 ` Quentin Perret
2020-11-16 10:31 ` Ard Biesheuvel
2020-11-16 12:05 ` Quentin Perret
2020-10-29 11:50 ` Mark Rutland
2020-10-29 11:58 ` Peter Zijlstra [this message]
2020-10-29 13:30 ` Mark Rutland
2020-10-29 11:59 ` Ard Biesheuvel
2020-10-29 13:21 ` Mark Rutland
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