From: Arnd Bergmann <arnd@kernel.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>, Jian Cai <jiancai@google.com>,
Guenter Roeck <linux@roeck-us.net>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@suse.de>,
Eric Dumazet <eric.dumazet@gmail.com>,
Juergen Gross <jgross@suse.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Thomas Gleixner <tglx@linutronix.de>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Ingo Molnar <mingo@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
He Ying <heying24@huawei.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] [v2] smp: fix smp_call_function_single_async prototype
Date: Thu, 6 May 2021 16:30:42 +0200 [thread overview]
Message-ID: <CAK8P3a36r9S_AYfp8Myf+3sfHvGVsBM36HmdoeVFi9BaNdS9Lg@mail.gmail.com> (raw)
In-Reply-To: <87pmy4qdb9.fsf@yhuang6-desk1.ccr.corp.intel.com>
On Thu, May 6, 2021 at 2:03 PM Huang, Ying <ying.huang@intel.com> wrote:
> Arnd Bergmann <arnd@kernel.org> writes:
> > On Thu, May 6, 2021 at 10:14 AM Huang, Ying <ying.huang@intel.com> wrote:
> >>
> >> We cannot avoid type cast in Linux kernel, such as container_of(), is
> >> there some difference here?
> >
> > container_of() does not cause any alignment problems. Assuming the outer
> > structure is aligned correctly, then the inner structure also is.
>
> So you think that the compiler may generate different code depends on
> the data structure alignment (8 vs. 32 here)? I think that it doesn't
> on x86. Do you know it does that on any architecture? But I understand
> that this is possible at least in theory.
It probably won't generate any different code because that would be silly, but
it's also not a good idea to rely on that. In theory the compiler might e.g.
construct an offset into the structure using a bitwise-or instruction instead of
an addition if the alignment tells it that the lower bits are always zero.
Arnd
next prev parent reply other threads:[~2021-05-06 14:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 21:12 [PATCH] [v2] smp: fix smp_call_function_single_async prototype Arnd Bergmann
2021-05-06 1:19 ` Huang, Ying
2021-05-06 7:54 ` Arnd Bergmann
2021-05-06 8:14 ` Huang, Ying
2021-05-06 8:30 ` Arnd Bergmann
2021-05-06 12:03 ` Huang, Ying
2021-05-06 14:30 ` Arnd Bergmann [this message]
2021-05-06 10:10 ` Peter Zijlstra
2021-05-06 13:48 ` [tip: locking/urgent] smp: Fix " tip-bot2 for Arnd Bergmann
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