linux-kernel - Re: [PATCH 21/26] tty: Convert tty

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Message-ID: <54072F75.70107@hurleysoftware.com>
Date:	Wed, 03 Sep 2014 11:10:45 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/26] tty: Convert tty_struct bitfield to bools

On 09/03/2014 08:19 AM, One Thousand Gnomes wrote:
>> Ahh. Thanks for the insight, Alan.
>>
>> But set_bit() et. al. will generate an incredible amount of churn;
>> what if I split the fields up to prevent false-sharing?
> 
> Do you feel lucky ;-)

Hahaha  :)

> I'd rather set_bit and friends were used. They exist largely for this
> kind of reason and they also have atomic test/set methods which may in
> the longer term be very useful.
> 
> Yes it is churn can't argue with that.

Yuck. There should be a better way. IXANY mode is suddenly going to
have a ton of unnecessary bus locks on x86.

Note the ctrl_status field is a byte as well, which can't be RMW'ed by
the bit-locked primitives, and definitely should not be aggregated with
any adjacent field.

Regards,
Peter Hurley

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