From: Peter Zijlstra <peterz@infradead.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Juergen Gross <jgross@suse.com>, Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data
Date: Fri, 4 Aug 2017 11:27:54 +0200 [thread overview]
Message-ID: <20170804092754.hyhbhyr2r4gonpu4@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <87mv7gytmk.fsf@yhuang-dev.intel.com>
On Fri, Aug 04, 2017 at 10:05:55AM +0800, Huang, Ying wrote:
> "Huang, Ying" <ying.huang@intel.com> writes:
> > Peter Zijlstra <peterz@infradead.org> writes:
> >> +struct __call_single_data {
> >> struct llist_node llist;
> >> smp_call_func_t func;
> >> void *info;
> >> unsigned int flags;
> >> };
> >>
> >> +typedef struct __call_single_data call_single_data_t
> >> + __aligned(sizeof(struct __call_single_data));
> >> +
> >
> > Another requirement of the alignment is that it should be the power of
> > 2. Otherwise, for example, if someone adds a field to struct, so that
> > the size becomes 40 on x86_64. The alignment should be 64 instead of
> > 40.
>
> Thanks Aaron, he reminded me that there is a roundup_pow_of_two(). So
> the typedef could be,
>
> typedef struct __call_single_data call_single_data_t
> __aligned(roundup_pow_of_two(sizeof(struct __call_single_data));
>
Yes, that would take away the requirement to play padding games with the
struct. Then again, maybe its a good thing to have to be explicit about
it.
If you see:
struct __call_single_data {
struct llist_node llist;
smp_call_func_t func;
void *info
int flags;
void *extra_field;
unsigned long __padding[3]; /* make align work */
};
that makes it very clear what is going on. In any case, we can delay
this part because the current structure is a power-of-2 for both ILP32
and LP64. So only the person growing this will have to deal with it ;-)
next prev parent reply other threads:[~2017-08-04 9:28 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-02 8:52 [PATCH 0/3] IPI: Avoid to use 2 cache lines for one call_single_data Huang, Ying
2017-08-02 8:52 ` [PATCH 1/3] percpu: Add alloc_percpu_aligned() Huang, Ying
2017-08-02 13:50 ` Christopher Lameter
2017-08-03 0:33 ` Huang, Ying
2017-08-02 8:52 ` [PATCH 2/3] iova: Use alloc_percpu_aligned() Huang, Ying
2017-08-02 8:52 ` [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data Huang, Ying
2017-08-02 10:18 ` Eric Dumazet
2017-08-02 10:53 ` Peter Zijlstra
2017-08-03 8:35 ` Huang, Ying
2017-08-03 8:57 ` Peter Zijlstra
2017-08-04 1:28 ` Huang, Ying
2017-08-04 2:05 ` Huang, Ying
2017-08-04 9:27 ` Peter Zijlstra [this message]
2017-08-05 0:47 ` Huang, Ying
2017-08-07 8:28 ` Peter Zijlstra
2017-08-08 4:30 ` Huang, Ying
2017-08-14 5:44 ` Huang, Ying
2017-08-28 5:19 ` Huang, Ying
2017-08-28 8:49 ` Peter Zijlstra
2017-08-29 14:23 ` [tip:locking/core] smp: Avoid using two cache lines for struct call_single_data tip-bot for Ying Huang
2017-08-04 9:20 ` [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data Peter Zijlstra
2017-08-02 13:54 ` [PATCH 0/3] " Christopher Lameter
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=20170804092754.hyhbhyr2r4gonpu4@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=aaron.lu@intel.com \
--cc=bp@suse.de \
--cc=eric.dumazet@gmail.com \
--cc=jgross@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=mpe@ellerman.id.au \
--cc=tglx@linutronix.de \
--cc=ying.huang@intel.com \
/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).