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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH v2] x86: use POPCNT for hweight<N>() when available
Date: Fri, 17 Mar 2023 12:22:02 +0100	[thread overview]
Message-ID: <ZBRNWhExetXH1OaS@Air-de-Roger> (raw)
In-Reply-To: <55a4a24d-7fac-527c-6bcf-8d689136bac2@suse.com>

On Mon, Jul 15, 2019 at 02:39:04PM +0000, Jan Beulich wrote:
> This is faster than using the software implementation, and the insn is
> available on all half-way recent hardware. Therefore convert
> generic_hweight<N>() to out-of-line functions (without affecting Arm)
> and use alternatives patching to replace the function calls.
> 
> Note that the approach doesn#t work for clang, due to it not recognizing
> -ffixed-*.

I've been giving this a look, and I wonder if it would be fine to
simply push and pop the scratch registers in the 'call' path of the
alternative, as that won't require any specific compiler option.

Thanks, Roger.


  parent reply	other threads:[~2023-03-17 11:22 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-15 14:39 [Xen-devel] [PATCH v2] x86: use POPCNT for hweight<N>() when available Jan Beulich
2020-05-14 14:05 ` Roger Pau Monné
2020-05-20  8:31   ` Jan Beulich
2020-05-20  9:31     ` Roger Pau Monné
2020-05-20 10:17       ` Jan Beulich
2020-05-20 10:28         ` Roger Pau Monné
2020-05-20 10:57           ` Jan Beulich
2020-05-20 11:43             ` Roger Pau Monné
2020-05-20 13:12               ` Jan Beulich
2020-05-20 17:18                 ` Roger Pau Monné
2020-05-22  9:58                   ` Jan Beulich
2020-05-22 10:19                     ` Roger Pau Monné
2023-03-17 11:22 ` Roger Pau Monné [this message]
2023-03-17 12:26   ` Andrew Cooper
2023-03-20  9:48     ` Jan Beulich
2023-03-21 14:57       ` Roger Pau Monné
2023-03-21 15:35         ` Jan Beulich
2023-03-21 15:44           ` Juergen Gross
2023-03-21 16:31           ` Roger Pau Monné
2023-03-21 16:41             ` Jan Beulich
2023-03-21 17:02               ` Roger Pau Monné

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