From: xinhui <xinhui.pan@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
waiman.long@hp.com
Subject: Re: [PATCH] locking/qrwlock: fix write unlock issue in big endian
Date: Fri, 03 Jun 2016 15:20:53 +0800 [thread overview]
Message-ID: <57512FD5.5020301@linux.vnet.ibm.com> (raw)
In-Reply-To: <20160602111505.GB3190@twins.programming.kicks-ass.net>
On 2016年06月02日 19:15, Peter Zijlstra wrote:
> On Thu, Jun 02, 2016 at 07:01:17PM +0800, xinhui wrote:
>>
>> On 2016年06月02日 18:44, Arnd Bergmann wrote:
>>> On Thursday, June 2, 2016 6:09:08 PM CEST Pan Xinhui wrote:
>>>> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
>>>> index 54a8e65..eadd7a3 100644
>>>> --- a/include/asm-generic/qrwlock.h
>>>> +++ b/include/asm-generic/qrwlock.h
>>>> @@ -139,7 +139,7 @@ static inline void queued_read_unlock(struct qrwlock *lock)
>>>> */
>>>> static inline void queued_write_unlock(struct qrwlock *lock)
>>>> {
>>>> - smp_store_release((u8 *)&lock->cnts, 0);
>>>> + (void)atomic_sub_return_release(_QW_LOCKED, &lock->cnts);
>>>> }
>>>
>>> Isn't this more expensive than the existing version?
>>>
>> yes, a little more expensive than the existing version
>
> Think 20+ cycles worse.
>
>> But does this is generic code, I am not sure how it will impact the performance on other archs.
>
> As always, you get to audit users of stuff you change. And here you're
> lucky, there's only 1.
>
yes, and hope there will be 2 :)
>> If you like
>> we calculate the correct address to set to NULL
>> say,
>> static inline void queued_write_unlock(struct qrwlock *lock)
>> {
>> u8 *wl = lock;
>>
>> #ifdef __BIG_ENDIAN
>> wl += 3;
>> #endif
>> smp_store_release(wl, 0);
>>
>> }
>
> No, that's horrible. Either lift __qrwlock into qrwlock_types.h or do
> what qspinlock does. And looking at that, we could make
agree.
> queued_spin_unlock() use the atomic_sub_return_relaxed() thing too I
> suppose, that generates slightly better code.
>
thanks for your suggestion.
I can have a try in queued_spin_unlock().
next prev parent reply other threads:[~2016-06-03 7:22 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-02 10:09 [PATCH] locking/qrwlock: fix write unlock issue in big endian Pan Xinhui
2016-06-02 10:44 ` Arnd Bergmann
2016-06-02 11:01 ` xinhui
2016-06-02 11:15 ` Peter Zijlstra
2016-06-03 7:20 ` xinhui [this message]
2016-06-02 11:02 ` Peter Zijlstra
2016-06-03 7:17 ` xinhui
[not found] ` <201606030718.u537FQg0009963@mx0a-001b2d01.pphosted.com>
2016-06-03 20:57 ` Waiman Long
2016-06-06 3:15 ` xinhui
2016-06-08 9:22 ` Will Deacon
2016-06-14 6:11 ` xinhui
2016-06-14 10:40 ` Will Deacon
2016-06-15 3:47 ` xinhui
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=57512FD5.5020301@linux.vnet.ibm.com \
--to=xinhui.pan@linux.vnet.ibm.com \
--cc=arnd@arndb.de \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=waiman.long@hp.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).