From: "Arnd Bergmann" <arnd@arndb.de>
To: "Peter Zijlstra" <peterz@infradead.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>
Cc: "Jonathan Corbet" <corbet@lwn.net>,
"Will Deacon" <will@kernel.org>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
dennis@kernel.org, "Tejun Heo" <tj@kernel.org>,
"Christoph Lameter" <cl@linux.com>,
"Heiko Carstens" <hca@linux.ibm.com>,
gor@linux.ibm.com, "Alexander Gordeev" <agordeev@linux.ibm.com>,
borntraeger@linux.ibm.com, "Sven Schnelle" <svens@linux.ibm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
"Joerg Roedel" <joro@8bytes.org>,
suravee.suthikulpanit@amd.com,
"Robin Murphy" <robin.murphy@arm.com>,
dwmw2@infradead.org, "Baolu Lu" <baolu.lu@linux.intel.com>,
"Herbert Xu" <herbert@gondor.apana.org.au>,
"David S . Miller" <davem@davemloft.net>,
"Pekka Enberg" <penberg@kernel.org>,
"David Rientjes" <rientjes@google.com>,
"Joonsoo Kim" <iamjoonsoo.kim@lge.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Roman Gushchin" <roman.gushchin@linux.dev>,
"Hyeonggon Yoo" <42.hyeyoo@gmail.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, linux-s390@vger.kernel.org,
iommu@lists.linux.dev, Linux-Arch <linux-arch@vger.kernel.org>,
linux-crypto@vger.kernel.org
Subject: Re: [PATCH v2 05/10] percpu: Wire up cmpxchg128
Date: Fri, 03 Feb 2023 18:25:04 +0100 [thread overview]
Message-ID: <24007667-1ff3-4c86-9c17-a361c3f9f072@app.fastmail.com> (raw)
In-Reply-To: <20230202152655.494373332@infradead.org>
On Thu, Feb 2, 2023, at 15:50, Peter Zijlstra wrote:
> In order to replace cmpxchg_double() with the newly minted
> cmpxchg128() family of functions, wire it up in this_cpu_cmpxchg().
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
I commented on this in the previous version but never got any
reply from you:
https://lore.kernel.org/all/1d88ba9f-5541-4b67-9cc8-a361eef36547@app.fastmail.com/
Unless I have misunderstood what you are doing, my concerns are
still the same:
> #define this_cpu_cmpxchg(pcp, oval, nval) \
> - __pcpu_size_call_return2(this_cpu_cmpxchg_, pcp, oval, nval)
> + __pcpu_size16_call_return2(this_cpu_cmpxchg_, pcp, oval, nval)
> #define this_cpu_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1,
> nval2) \
> __pcpu_double_call_return_bool(this_cpu_cmpxchg_double_, pcp1, pcp2,
> oval1, oval2, nval1, nval2)
Having a variable-length this_cpu_cmpxchg() that turns into cmpxchg128()
and cmpxchg64() even on CPUs where this traps (!X86_FEATURE_CX16) seems
like a bad design to me.
I would much prefer fixed-length this_cpu_cmpxchg64()/this_cpu_cmpxchg128()
calls that never trap but fall back to the generic version on CPUs that
are lacking the atomics.
Arnd
next prev parent reply other threads:[~2023-02-03 17:51 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-02 14:50 [PATCH v2 00/10] Introduce cmpxchg128() -- aka. the demise of cmpxchg_double() Peter Zijlstra
2023-02-02 14:50 ` [PATCH v2 01/10] cyrpto/b128ops: Remove struct u128 Peter Zijlstra
2023-02-02 20:21 ` H. Peter Anvin
2023-02-03 1:06 ` Herbert Xu
2023-02-02 14:50 ` [PATCH v2 02/10] types: Introduce [us]128 Peter Zijlstra
2023-02-03 3:37 ` Herbert Xu
2023-02-02 14:50 ` [PATCH v2 03/10] arch: Introduce arch_{,try_}_cmpxchg128{,_local}() Peter Zijlstra
2023-02-02 17:04 ` Heiko Carstens
2023-02-03 16:52 ` Mark Rutland
2023-02-02 14:50 ` [PATCH v2 04/10] instrumentation: Wire up cmpxchg128() Peter Zijlstra
2023-02-03 16:55 ` Mark Rutland
2023-02-02 14:50 ` [PATCH v2 05/10] percpu: Wire up cmpxchg128 Peter Zijlstra
2023-02-02 17:05 ` Heiko Carstens
2023-02-03 17:02 ` Mark Rutland
2023-02-03 17:25 ` Arnd Bergmann [this message]
2023-02-06 11:24 ` Peter Zijlstra
2023-02-06 12:14 ` Peter Zijlstra
2023-02-06 12:48 ` Peter Zijlstra
2023-02-06 13:20 ` Arnd Bergmann
2023-02-06 12:19 ` Arnd Bergmann
2023-02-02 14:50 ` [PATCH v2 06/10] x86,amd_iommu: Replace cmpxchg_double() Peter Zijlstra
2023-02-02 14:50 ` [PATCH v2 07/10] x86,intel_iommu: " Peter Zijlstra
2023-02-03 2:51 ` Baolu Lu
2023-02-02 14:50 ` [PATCH v2 08/10] slub: " Peter Zijlstra
2023-02-08 13:31 ` Hyeonggon Yoo
2023-02-02 14:50 ` [PATCH v2 09/10] arch: Remove cmpxchg_double Peter Zijlstra
2023-02-08 13:44 ` Hyeonggon Yoo
2023-02-02 14:50 ` [PATCH v2 10/10] s390/cpum_sf: Convert to cmpxchg128() Peter Zijlstra
2023-02-02 17:05 ` Heiko Carstens
2023-02-02 19:39 ` [PATCH v2 00/10] Introduce cmpxchg128() -- aka. the demise of cmpxchg_double() Linus Torvalds
2023-02-02 22:45 ` David Laight
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=24007667-1ff3-4c86-9c17-a361c3f9f072@app.fastmail.com \
--to=arnd@arndb.de \
--cc=42.hyeyoo@gmail.com \
--cc=agordeev@linux.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=baolu.lu@linux.intel.com \
--cc=boqun.feng@gmail.com \
--cc=borntraeger@linux.ibm.com \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=cl@linux.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=davem@davemloft.net \
--cc=dennis@kernel.org \
--cc=dwmw2@infradead.org \
--cc=gor@linux.ibm.com \
--cc=hca@linux.ibm.com \
--cc=herbert@gondor.apana.org.au \
--cc=hpa@zytor.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=iommu@lists.linux.dev \
--cc=joro@8bytes.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-s390@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=penberg@kernel.org \
--cc=peterz@infradead.org \
--cc=rientjes@google.com \
--cc=robin.murphy@arm.com \
--cc=roman.gushchin@linux.dev \
--cc=suravee.suthikulpanit@amd.com \
--cc=svens@linux.ibm.com \
--cc=tglx@linutronix.de \
--cc=tj@kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=vbabka@suse.cz \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/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).