linux-kernel - Re: [PATCH v7 01/11] timekeeping: move multigrain timestamp floor handling into timekeeper

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Message-ID: <CANDhNCpPr-MvQhV7P6at9fQ-UpM_Q9R+S9oVqjHyguOgzrrZZQ@mail.gmail.com>
Date: Fri, 13 Sep 2024 12:17:26 -0700
From: John Stultz <jstultz@...gle.com>
To: Jeff Layton <jlayton@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Stephen Boyd <sboyd@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Jonathan Corbet <corbet@....net>, 
	Chandan Babu R <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>, 
	"Theodore Ts'o" <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, Chris Mason <clm@...com>, 
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>, Hugh Dickins <hughd@...gle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Chuck Lever <chuck.lever@...cle.com>, 
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-xfs@...r.kernel.org, 
	linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org, 
	linux-nfs@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v7 01/11] timekeeping: move multigrain timestamp floor
 handling into timekeeper

On Fri, Sep 13, 2024 at 12:06 PM Jeff Layton <jlayton@...nel.org> wrote:
> On Fri, 2024-09-13 at 11:59 -0700, John Stultz wrote:
> > > +/**
> > > + * ktime_get_real_ts64_mg - attempt to update floor value and return result
> > > + * @ts:                pointer to the timespec to be set
> > > + * @cookie:    opaque cookie from earlier call to ktime_get_coarse_real_ts64_mg()
> > > + *
> > > + * Get a current monotonic fine-grained time value and attempt to swap
> > > + * it into the floor using @cookie as the "old" value. @ts will be
> > > + * filled with the resulting floor value, regardless of the outcome of
> > > + * the swap.
> >
> > I'd add more detail here to clarify that this can return a coarse
> > floor value if the cookie is stale.
> >
>
> Sure, or I can just drop the cookie, if that's better.

That seems like the simpler approach, but I don't have a sense of the
actual performance impact, so I'll leave that decision to you.

thanks
-john