On Thu, May 24, 2018 at 12:06 PM Greg KH gregkh@linuxfoundation.org wrote:
On Thu, May 24, 2018 at 10:27:59AM -0700, Hugh Dickins wrote:
On Thu, May 24, 2018 at 4:28 AM Greg KH gregkh@linuxfoundation.org
wrote:
On Thu, May 24, 2018 at 04:17:12AM -0700, Hugh Dickins wrote:
Thu, May 24, 2018 at 4:06 AM Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
On Thu, May 24, 2018 at 12:50:11PM +0200, Jan Kara wrote:
On Thu 24-05-18 11:38:27, Greg Kroah-Hartman wrote: > 4.4-stable review patch. If anyone has any objections, please
let me
know.
Just one objection: Why does stable care about this (and the
previous
patch)? I've checked the stable queue and I don't see anything
that
would
have these patches as a prerequisite. And on their own, they are
only
cleanups without substantial gains.
There's a small gain here:
> paralleldd > 4.4.0
4.4.0
> vanilla
avoidlock
> Amean Elapsd-1 5.28 ( 0.00%) 5.15 (
2.50%)
> Amean Elapsd-4 5.29 ( 0.00%) 5.17 (
2.12%)
> Amean Elapsd-7 5.28 ( 0.00%) 5.18 (
1.78%)
> Amean Elapsd-12 5.20 ( 0.00%) 5.33 (
-2.50%)
> Amean Elapsd-21 5.14 ( 0.00%) 5.21 (
-1.41%)
> Amean Elapsd-30 5.30 ( 0.00%) 5.12 (
3.38%)
> Amean Elapsd-48 5.78 ( 0.00%) 5.42 (
6.21%)
> Amean Elapsd-79 6.78 ( 0.00%) 6.62 (
2.46%)
> Amean Elapsd-110 9.09 ( 0.00%) 8.99 (
1.15%)
> Amean Elapsd-128 10.60 ( 0.00%) 10.43 (
1.66%)
> > The impact is small but intuitively, it makes sense to avoid
unnecessary
> calls to lock_page.
Yes, it's small, but it's marked in the SLES kernel as "needs to
be
merged into stable", so obviously it matters to someone :)
Hmm. I had the same reaction to these two as Jan, but assumed that
they
made applying later patches easier, and didn't take the trouble he
did
to
find that's not so.
I've no wish to be disputatious, but it does seem that the
definition of
"stable" has changed, and not necessarily for the better, if it's
now a
home for small gains: I thought we left those to upstream.
This is in the SLES kernel for a reason, and again, it's in the
section
that says "this should be pushed to stable". So if it's good enough
for
the SLES kernel, why isn't it good enough for all users of this kernel tree?
If you all think it should be dropped in both places, that's fine with me :)
I think they are perfectly fine in SLES: folding in good work is a part
of
what distros are about.
And it's also what stable is for. We have had backports of performance improvements in the past, along with lots of other things over the years. This is a performance improvement. A tiny one, yes, but getting rid of a lock is a good thing, and I picked it up as part of my review of what a distro decided was worth adding for their users, as that's a huge signal that might be of value to others.
But I cannot find anything in stable-kernel-rules.rst that would admit
them
- perhaps that's just out of date?
Nope, that's the list I use to say "no" to. You can't describe everything in that file, it's a judgement call.
If -stable is to be a compendium of "this looks nice, you might like to include it", so be it: but the rules should then be updated.
This is a "a bunch of people I trust took it in their kernel, and it's been running on zillion of machines for a while and causes no harm and a slight benefit, so let's add it!" type of thing. It's not the only patch in this series that was like that, but for some reason this one is the one the triggered the debate, which is funny to me as this does have numbers in it showing that it is an improvement :)
Thank you for looking after the -stable trees: please let me not waste your time any further. I have no specific objection to the two patches, which are certainly not egregious offenders. But I do still find the disconnect between stable-kernel-rules.rst and reality confusing - or perhaps I just find reality confusing :)
Hugh