linux-kernel - Re: locking changes in tty broke low latency feature

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <53067C50.9010708@hurleysoftware.com>
Date:	Thu, 20 Feb 2014 17:06:08 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Grant Edwards <grant.b.edwards@...il.com>
CC:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-rt-users@...r.kernel.org,
	Hal Murray <murray+fedora@...64-139-1-69.sjc.megapath.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Stanislaw Gruszka <sgruszka@...hat.com>
Subject: Re: locking changes in tty broke low latency feature

On 02/20/2014 02:33 PM, Grant Edwards wrote:
> On 2014-02-20, Peter Hurley <peter@...leysoftware.com> wrote:
>> Sender completes 2000 loops in 160ms total run time;
>> that's 80us average per complete round-trip.
>
> If I understand correctly, that 80us _includes_ the actual time for
> the bits on the wire (which means the actual "baud rate" involved is
> high enough that it's negligible).

Yes, 80us includes the transmit time.

>> I think this shows that low_latency is unnecessary and should
>> just be removed/ignored by the tty core.
>
> If that's the sort of latency that you get for typical kernel
> configurations for typical distros, then I agree that the low_latency
> flag is not needed by the tty later.

Stock ubuntu kernel config but preempt and 250hz (and debugging stuff).

> However, it might still be useful for the lower-level tty or
> serial-core driver to control CPU usage vs. latency trade-offs (for
> exaple, one of my drivers uses it to decide where to set the rx FIFO
> threshold).

Sure, it could be left for driver consumption.

Regards,
Peter Hurley

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/