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Groups > linux.kernel > #1525746
| From | David Howells <dhowells@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available |
| Date | 2016-11-19 00:00 +0100 |
| Message-ID | <sF0it-4V9-9@gated-at.bofh.it> (permalink) |
| References | (1 earlier) <sEvol-1nz-5@gated-at.bofh.it> <sEvol-1nz-3@gated-at.bofh.it> <sEEBj-7vt-7@gated-at.bofh.it> <sEI2d-1vi-11@gated-at.bofh.it> <sEZw5-4AG-1@gated-at.bofh.it> |
| Organization | Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 |
Dave Chinner <david@fromorbit.com> wrote:
> And when we start thinking in those timeframes, an
> increase in timestamp resoultion of at least another 10e-3 is
> likely....
Is it, though? To be useful, surely you have to be able to jam quite a few
instructions into a 1ns block, including memory accesses.
Rather than providing:
struct timestamp {
__s64 seconds;
__s64 femtoseconds;
};
which would require 64-bit divisions to get nanosecond timestamps that we do
actually use, I would lean towards:
struct timestamp {
__s64 seconds;
__s32 nanoseconds;
__s32 femtoseconds;
};
where the fields are, in effect, additive. Which means I could represent this
as:
__s64 stx_atime_s; /* Last access time */
__s64 stx_btime_s; /* File creation time */
__s64 stx_ctime_s; /* Last attribute change time */
__s64 stx_mtime_s; /* Last data modification time */
__s32 stx_atime_ns; /* Last access time (ns part) */
__s32 stx_btime_ns; /* File creation time (ns part) */
__s32 stx_ctime_ns; /* Last attribute change time (ns part) */
__s32 stx_mtime_ns; /* Last data modification time (ns part) */
and then add:
__s32 stx_atime_fs; /* Last access time (fs part) */
__s32 stx_btime_fs; /* File creation time (fs part) */
__s32 stx_ctime_fs; /* Last attribute change time (fs part) */
__s32 stx_mtime_fs; /* Last data modification time (fs part) */
later.
If we *really* do want to allow for atto- or femto- second resolution
timestamps (and you've still not entirely convinced me that it's going to be
necessary - the speed of signal propagation still has an ungetroundable
limit), then we could stick the space in now - but I think it's likely to
remain dead space.
Maybe we should switch to Windows-style timestamp resolution:
struct timestamp {
__s64 hundred_ns; /* Time in 100ns increments */
__s32 femtoseconds; /* Additional fs component */
};
> > Using the existing FS_*_FL flags as initial values is not worse than
> > starting with any other arbitrary values for the flags.
>
> Except it starts with a sparse set of flags for no good reason.
Actually, a very good reason. You can map those flags, on ext4 at least, with
a load, an AND and an OR. Three instructions[*]. If the bits don't
correspond, it gets more expensive (4-5 instructions per bit + 1).
[*] Leastways, it *should* be three instructions, but gcc fails to optimise it
correctly. I have a bz logged for this.
David
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[RFC][PATCH 0/4] Enhanced file stat system call David Howells <dhowells@redhat.com> - 2016-11-17 15:00 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call David Howells <dhowells@redhat.com> - 2016-11-17 18:10 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call David Howells <dhowells@redhat.com> - 2016-11-17 18:10 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call bfields@fieldses.org (J. Bruce Fields) - 2016-11-17 21:10 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call Andreas Dilger <adilger@dilger.ca> - 2016-11-18 03:50 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call NeilBrown <neilb@suse.com> - 2016-11-18 05:40 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-11-18 14:50 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call David Howells <dhowells@redhat.com> - 2016-11-18 14:50 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call Michael Kerrisk <mtk.manpages@gmail.com> - 2016-11-17 18:20 +0100
[PATCH 3/4] statx: NFS: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-11-17 18:20 +0100
[PATCH 2/4] statx: Ext4: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-11-17 18:20 +0100
Re: [PATCH 2/4] statx: Ext4: Return enhanced file attributes Andreas Dilger <adilger@dilger.ca> - 2016-11-18 04:40 +0100
[PATCH 4/4] statx: AFS: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-11-17 18:20 +0100
Re: [PATCH 4/4] statx: AFS: Return enhanced file attributes Andreas Dilger <adilger@dilger.ca> - 2016-11-18 09:30 +0100
Re: [PATCH 4/4] statx: AFS: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-11-18 09:50 +0100
Re: [RFC][PATCH 0/4] Enhanced file stat system call One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-11-17 19:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-18 00:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Andreas Dilger <adilger@dilger.ca> - 2016-11-18 04:30 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 11:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-18 23:10 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-19 00:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-19 23:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-22 11:40 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Jeff Layton <jlayton@redhat.com> - 2016-11-22 15:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-22 22:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-11-21 15:40 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-21 21:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 10:40 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Jeff Layton <jlayton@poochiereds.net> - 2016-11-18 18:20 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 19:10 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Jeff Layton <jlayton@redhat.com> - 2016-11-18 20:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 20:10 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 10:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-18 22:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 23:30 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 11:30 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-18 22:30 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 22:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Dave Chinner <david@fromorbit.com> - 2016-11-18 23:20 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-11-19 11:30 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 09:50 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Jeff Layton <jlayton@redhat.com> - 2016-11-18 13:10 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-11-18 10:00 +0100
Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available Andreas Dilger <adilger@dilger.ca> - 2016-11-18 10:30 +0100
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