linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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Date:	Thu, 16 Apr 2015 12:31:51 +0200
From:	Daniel Mack <daniel@...que.org>
To:	Andy Lutomirski <luto@...capital.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>, Tom Gundersen <teg@...m.no>,
	Jiri Kosina <jkosina@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

On 04/16/2015 12:11 AM, Andy Lutomirski wrote:
> Also, getting the really high performance stuff right would be nice.
> Binder has one thing going for it (IIRC -- I've talked about it to
> some of the authors, but I've never so much as glanced at the code):
> it has a primitive to send and wait for a reply.  This reduces the
> load on scheduler.

kdbus has the same thing, we call it a synchronous reply. That concept
is actually comprehensively explained in kdbus.message(7):

  By default, all calls to kdbus are considered asynchronous,
  non-blocking. However, as there are many use cases that need
  to wait for a remote peer to answer a method call, there's a
  way to send a message and wait for a reply in a synchronous
  fashion. This is what the KDBUS_SEND_SYNC_REPLY controls. The
  KDBUS_CMD_SEND ioctl will block until the reply has arrived,
  the timeout limit is reached, in case the remote connection
  was shut down, or if interrupted by a signal before any reply;
  see signal(7). The offset of the reply message in the sender's
  pool is stored in in offset_reply when the ioctl has returned
  without error. Hence, there is no need for another KDBUS_CMD_RECV
  ioctl or anything else to receive the reply.

Thanks,
Daniel

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