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From: Julien Grall <julien@xen.org>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Cc: "Jan Beulich" <JBeulich@suse.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Bertrand Marquis" <bertrand.marquis@arm.com>
Subject: Re: [PATCH 3/5] xen/sort: Switch to an extern inline implementation
Date: Fri, 12 Nov 2021 09:39:51 +0000	[thread overview]
Message-ID: <b3dd2e88-6b32-f066-1f6e-d638ade23826@xen.org> (raw)
In-Reply-To: <20211111175740.23480-4-andrew.cooper3@citrix.com>

Hi Andrew,

On 11/11/2021 17:57, Andrew Cooper wrote:
> There are exactly 3 callers of sort() in the hypervisor.
> 
> Both arm callers pass in NULL for the swap function.  While this might seem
> like an attractive option at first, it causes generic_swap() to be used which
> forced a byte-wise copy.  Provide real swap functions which the compiler can
> optimise sensibly.
> 
> Furthermore, use of function pointers in tight loops like that can be very bad
> for performance.  Implement sort() as extern inline, so the optimiser can
> judge whether to inline things or not.
> 
> On x86, the diffstat shows how much of a better job the compiler can do when
> it is able to see the cmp/swap implementations.

For completness, here the Arm bloat-o-meter:

add/remove: 0/5 grow/shrink: 2/0 up/down: 928/-660 (268)
Function                                     old     new   delta
boot_fdt_info                                640    1132    +492
register_mmio_handler                        292     728    +436
u32_swap                                      20       -     -20
generic_swap                                  40       -     -40
cmp_mmio_handler                              44       -     -44
cmp_memory_node                               44       -     -44
sort                                         512       -    -512
Total: Before=966915, After=967183, chg +0.03%

Cheers,

-- 
Julien Grall


  parent reply	other threads:[~2021-11-12  9:40 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 [this message]
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
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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