Re: [PATCH v8 01/11] timekeeping: move multigrain timestamp floor handling into timekeeper

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, Oct 01 2024 at 05:45, Jeff Layton wrote:
> On Mon, 2024-09-30 at 23:35 +0200, Thomas Gleixner wrote:
>> > I certainly wouldn't rule out a workqueue job calling that function,
>> > but this is something we do while dirtying an inode, and that's not
>> > typically done in interrupt context.
>> 
>> The reason I'm asking is that if it's always syscall context,
>> i.e. write() or io_uring()/RPC request etc., then you can avoid the
>> whole global floor value dance and make it strictly per thread, which
>> simplifies the exercise significantly.
>> 
>
> I'm not sure I follow what you're proposing here.
>
> Consider two threads doing writes serially to different files. IOW, the
> second thread enters the write() syscall after the first thread returns
> from its write(). In that situation, the second timestamp mustn't
> appear to be earlier than the first (assuming no backward clock jump,
> of course).
>
> How would we ensure that with only per-thread structures?

Bah. Right. Ignore my sleep deprived rambling.