From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 5/5] x86/ioapic: Drop function pointers from __ioapic_{read,write}_entry()
Date: Fri, 12 Nov 2021 11:43:53 +0100 [thread overview]
Message-ID: <e220b6f2-3cb9-e7b0-6b74-4b266e4e7fb6@suse.com> (raw)
In-Reply-To: <20211111175740.23480-6-andrew.cooper3@citrix.com>
On 11.11.2021 18:57, Andrew Cooper wrote:
> Function pointers are expensive, and the raw parameter is a constant from all
> callers, meaning that it predicts very well with local branch history.
The code change is fine, but I'm having trouble with "all" here: Both
functions aren't even static, so while callers in io_apic.c may
benefit (perhaps with the exception of ioapic_{read,write}_entry(),
depending on whether the compiler views inlining them as warranted),
I'm in no way convinced this extends to the callers in VT-d code.
Further ISTR clang being quite a bit less aggressive about inlining,
so the effects might not be quite as good there even for the call
sites in io_apic.c.
Can you clarify this for me please?
Jan
next prev parent reply other threads:[~2021-11-12 10:44 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 17:57 [PATCH 0/5] xen: various function pointer cleanups Andrew Cooper
2021-11-11 17:57 ` [PATCH 1/5] xen/domain: Remove function pointers from domain pause helpers Andrew Cooper
2021-11-12 9:36 ` Julien Grall
2021-11-18 1:47 ` Andrew Cooper
2021-11-18 9:28 ` Julien Grall
2021-11-12 9:57 ` Jan Beulich
2021-11-17 23:31 ` Andrew Cooper
2021-11-15 10:13 ` Bertrand Marquis
2021-11-15 10:20 ` Jan Beulich
2021-11-15 10:23 ` Bertrand Marquis
2021-11-15 10:55 ` Jan Beulich
2021-11-15 11:23 ` Bertrand Marquis
2021-11-15 14:11 ` Julien Grall
2021-11-15 14:45 ` Bertrand Marquis
2021-11-16 0:41 ` Stefano Stabellini
2021-11-16 7:15 ` Jan Beulich
2021-11-11 17:57 ` [PATCH 2/5] xen/domain: Improve pirq handling Andrew Cooper
2021-11-12 10:16 ` Jan Beulich
2021-11-11 17:57 ` [PATCH 3/5] xen/sort: Switch to an extern inline implementation Andrew Cooper
2021-11-11 18:15 ` Julien Grall
2021-11-16 0:36 ` Stefano Stabellini
2021-11-16 0:41 ` Andrew Cooper
2021-12-17 15:56 ` Andrew Cooper
2021-12-17 16:15 ` Julien Grall
2021-11-12 9:39 ` Julien Grall
2021-11-12 10:25 ` Jan Beulich
2021-11-11 17:57 ` [PATCH 4/5] xen/wait: Remove indirect jump Andrew Cooper
2021-11-12 10:35 ` Jan Beulich
2021-11-11 17:57 ` [PATCH 5/5] x86/ioapic: Drop function pointers from __ioapic_{read,write}_entry() Andrew Cooper
2021-11-12 10:43 ` Jan Beulich [this message]
2021-11-18 0:32 ` Andrew Cooper
2021-11-18 9:06 ` Jan Beulich
2021-11-18 9:07 ` Jan Beulich
2021-11-18 17:33 ` Andrew Cooper
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