linux-kernel - Re: [PATCH v2 1/4] aio: add aio_kernel

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Message-ID: <CACVXFVNLQegYD2RHO9EVCVNcYE0hgn5xXXJPRud9kM8zaCYNGQ@mail.gmail.com>
Date:	Tue, 27 Jan 2015 21:57:47 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	Maxim Patlasov <mpatlasov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"open list:AIO" <linux-aio@...ck.org>
Subject: Re: [PATCH v2 1/4] aio: add aio_kernel_() interface

On Tue, Jan 27, 2015 at 1:00 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Tue, Jan 27, 2015 at 12:18:23AM +0800, Ming Lei wrote:
>> > Also it might make sense to just offer aio_kernel_read/write intefaces
>> > instead of the common submit wrapper, as that's much closer to other
>> > kernel APIs, e.g.
>> >
>> > int aio_kernel_read(struct kiocb *iocb, struct file *file,
>> >                 struct iov_iter *iter, loff_t off,
>> >                 void (*complete)(struct kiocb *iocb, long res));
>> > int aio_kernel_write(struct kiocb *iocb, struct file *file,
>> >                 struct iov_iter *iter, loff_t off,
>> >                 void (*complete)(struct kiocb *iocb, long res));
>>
>> It is like style of sync APIs, looks submit/complete is common
>> for async APIs, like io_submit().
>
> io_submit is a fairly horrible API.  While Posix AIO isn't too much
> better it does have separate APIs for read/write.  Given that there
> isn't much code shared I'd keep an API that feels familar.

But from performance view, the two APIs of aio_kernel_read()
and aio_kernel_write() aren't good because both need
5 parameters which can't be held in registers and they are
often called from single thread context, not like synchronized
read() and write().

Also aio_kernel_init_rw() can be moved to header file as inline
to avoid too many parameters.

Thanks,
Ming Lei
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