linux-kernel - Re: [PATCH v2 1/2] sched/wait: Add wait

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Date:   Tue, 24 Sep 2019 09:44:22 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Ingo Molnar <mingo@...hat.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sched/wait: Add wait_threshold


On 23/09/2019 22:27, Peter Zijlstra wrote:
> 
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
> 
> On Mon, Sep 23, 2019 at 07:37:46PM +0300, Pavel Begunkov wrote:
>> Just in case duplicating a mail from the cover-letter thread:
> 
> Just because every patch should have a self contained and coherent
> Changelog.

Well, I will expand the patch description, if we agree on the
implementation (at least conceptually).


>>
>> BTW, this monster is mostly a copy-paste from wait_event_*(),
>> wait_bit_*(). We could try to extract some common parts from these
>> three, but that's another topic.
> 
> I don't think that is another topic at all. It is a quality of
> implementation issue. We already have too many copies of all that (3).

For example, ___wait_event() is copied in ___wait_var_event(). Instead
it could accept a wait entry generator or just accept entry from above
and be reused in both cases. I've had such a patch, but want to think
what else could be done.

e.g.
```
#define generic_wait_event(ENTRY_GEN, ...)
	ENTRY_GEN(wq_entry_name);
	do_wait_event(wq_entry_name);

#define WBQ_ENTRY_GEN(name)
	struct wait_bit_queue_entry tmp = WBQ_INITIALIZER;
	struct wait_queue_entry	name = &tmp->wq_entry;
```


> 
> So basically you want to fudge the wake function to do the/a @cond test,
> not unlike what wait_bit already does, but differenly.
> 
Yes

> I'm really rather annoyed with C for not having proper lambda functions;
> that would make all this so much easier. Anyway, let me have a poke at
> this in the morning, it's late already.
> 
> Also, is anything actually using wait_queue_entry::private ? I'm
> not finding any in a hurry.
> 
> 

-- 
Yours sincerely,
Pavel Begunkov



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