linux-kernel - Re: Slow pty's (was Re: libdivecomputer interfaces?)

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Date:	Thu, 10 Jun 2010 15:30:20 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Brian Bloniarz <bmb@...enacr.com>
Cc:	Chris Wedgwood <cw@...f.org>, Greg KH <gregkh@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Jef Driesen <jefdriesen@...enet.be>,
	linux-kernel@...r.kernel.org
Subject: Re: Slow pty's (was Re: libdivecomputer interfaces?)

On Thu, Jun 10, 2010 at 3:25 PM, Brian Bloniarz <bmb@...enacr.com> wrote:
> On 06/10/2010 02:10 PM, Chris Wedgwood wrote:
>>
>> this might not be related, but i have slow serial ports with NOHZ that
>> goes away when i revert 39c0cbe2150cbd848a25ba6cdb271d1ad46818ad.
>
> Unrelated or not, I think Chris is right about this. Somewhere before
> -rc1, the emulated serial console on my KVM instance became slow
> to echo input. I just tested with the commit reverted and it's
> back to normal.

I suspect it's related. The tty subsystem clearly ends up depending on
the timer tick to move things forward even if there are pending
readers. So I suspect the slowness is very much related to the same
issue.

                     Linus
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