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From: Jens Axboe <>
To: Hristo Venev <>
Subject: Re: [PATCH] io_uring: allocate the two rings together
Date: Thu, 29 Aug 2019 09:04:59 -0600
Message-ID: <> (raw)
In-Reply-To: <>

On 8/27/19 1:35 PM, Hristo Venev wrote:
> Sorry for the duplicate reply, I forgot to CC the mailing list.
> On Tue, 2019-08-27 at 09:50 -0600, Jens Axboe wrote:
>> Outside of going for a cleanup, have you observed any wins from this
>> change?
> I haven't ran any interesting benchmarks. The cp examples in liburing
> are running as fast as before, at least on x86_64.
> Do you think it makes sense to tell userspace that the sq and cq mmap
> offsets now mean the same thing? We could add a flag set by the kernel
> to io_uring_params.

Not sure, there isn't a whole lot of overhead associated with having
to do two mmaps vs just one.

If you wanted to, the best approach would be to change one of the
io_uring_params reserved fields to be a feature field or something
like that. As features get added, we could flag them there. Then
the app could do:

io_uring_setup(depth, &params);
if (params.features & IORING_FEAT_SINGLE_MMAP)
	mmap rings individually

and so forth.

Jens Axboe

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-26 17:23 Hristo Venev
2019-08-27 15:50 ` Jens Axboe
2019-08-27 19:35   ` Hristo Venev
2019-08-29 15:04     ` Jens Axboe [this message]
2019-09-06 16:26       ` Jens Axboe
2019-09-06 19:12         ` [PATCH 1/2] liburing/test: There are now 4 reserved fields Hristo Venev
2019-09-06 19:12           ` [PATCH 2/2] liburing: Use the single mmap feature Hristo Venev
2019-09-06 19:30             ` Jens Axboe
2019-09-06 19:24           ` [PATCH 1/2] liburing/test: There are now 4 reserved fields Jens Axboe

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