On Wed, Jan 16, 2019 at 07:15:15AM +0900, Akira Yokosawa wrote:
> On 2019/01/15 09:43:04 -0800, Paul E. McKenney wrote:
> > On Wed, Jan 16, 2019 at 12:32:52AM +0900, Akira Yokosawa wrote:
> >> On 2019/01/14 17:33:37 -0800, Paul E. McKenney wrote:
> >>> On Sun, Jan 13, 2019 at 06:10:24PM -0800, Paul E. McKenney wrote:
> >>>> On Mon, Jan 14, 2019 at 08:28:27AM +0900, Akira Yokosawa wrote:
> >>>>> >From 7b69a9b37ba9a73a50aad5cbb097235ddfe75870 Mon Sep 17 00:00:00 2001
> >>>>> From: Akira Yokosawa <akiyks@xxxxxxxxx>
> >>>>> Date: Mon, 14 Jan 2019 07:25:14 +0900
> >>>>> Subject: [PATCH 0/6] Simplify hash_resize.c
> >>>>>
> >>>>> Hi Paul,
> >>>>>
> >>>>> This patch set updates hash_resize.c, which you suggested for me to
> >>>>> take over, and the related text.
> >>>>>
> >>>>> I added a couple of Quick Quizzes as well, and in one of them,
> >>>>> I included your version of hash_resize.c.
> >>>>>
> >>>>> Patch #1 updates hash_resize.c in the way I suggested. Note that
> >>>>> in this update, "#ifndef FCV_SNIPPET" blocks are used to hide
> >>>>> code for debugging (hash value checks) in code snippets.
> >>>>> This code can actually be compiled with "-DFCV_SNIPPET" to see
> >>>>> the performance without hash value checks.
> >>>>>
> >>>>> Patch #2 adds a couple of Quick Quizzes. Your version of hash_resize.c
> >>>>> is added as hash_resize_s.c.
> >>>>>
> >>>>> Patch #3 removes unnecessary folding in a code snippet.
> >>>>>
> >>>>> Patch #4 adjusts a few sentence to the simpler approach.
> >>>>>
> >>>>> Patch #5 adds another Quick Quiz.
> >>>>>
> >>>>> Patch #6 adds an "#error" directive for the lack of rcu_barrier().
> >>>>>
> >>>>> All of the updates in text would need your native eyes to be polished.
> >>>>
> >>>> Nice! Queued and pushed, thank you! I will review and send any
> >>>> needed update by end of tomorrow, Pacific Time.
> >>>
> >>> Here is a summary of changes:
> >>>
> >>> o Move the ht_lock_state structure definition to follow the ht
> >>> structure, matching the order of discussion in the text.
> >>> Everything seems to build and run OK with this change.
> >>> Also illustrates the advantages of line labels! ;-)
> >>>
> >>> o I considered inlining ht_search_bucket() into its only caller
> >>> in hashtab_lookup(), but decided against it. More flexibility
> >>> for change with it as is.
> >>>
> >>> o I added ht_search_bucket() to the in-text list of things
> >>> permitting lookups and modifications to run concurrently with
> >>> a resize operation.
> >>>
> >>> o I tweaked the description of hashtab_lock_mod(), hashtab_unlock_mod(),
> >>> hashtab_add(), and hashtab_del().
> >>>
> >>> o I tweaked the QQ asking about searches missing adds during resizes.
> >>>
> >>> o English is strange, so "Less Changes" must become "Fewer Changes".
> >>
> >> Sigh, I thought I knew this rule... Thanks for the fix.
> >>
> >>>
> >>> o I put the long labels on a single line out of paranoia.
> >>>
> >>> I pushed these out on a working branch named paulmck.2019.01.14a. Please
> >>> let me know whether I messed anything up, and once it looks good to you,
> >>> I will pull these two commits into the master branch.
> >>
> >> There is an irrelevant clause added in an answer to a QQ.
> >> See below for my suggestion. It doesn't sound fluent enough, though.
> >
> > Good catch!
> >
> > How does the following amended patch look?
>
> It looks perfect!
Very good, thank you! I have merged it and pushed the result.
Thanx, Paul
> Thanks, Akira
>
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > commit 731c855ab11b9601a40324c6ef6b5ced6d7833e9
> > Author: Akira Yokosawa <akiyks@xxxxxxxxx>
> > Date: Tue Jan 15 23:52:27 2019 +0900
> >
> > datastruct/hash: Fix irrelevant clause in answer to quick quiz
> >
> > hashtab_lookup() is not affected by the reordering of ->hbp[] and
> > ->hls_idx[]. Instead, mention the increase of cost at the earlier
> > explanation of hashtab_lookup().
> >
> > Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
> > [ paulmck: Wordsmithing. ]
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
> >
> > diff --git a/datastruct/datastruct.tex b/datastruct/datastruct.tex
> > index d1fde2c7535e..985021e927a8 100644
> > --- a/datastruct/datastruct.tex
> > +++ b/datastruct/datastruct.tex
> > @@ -1189,13 +1189,15 @@ a concurrent resize operation.
> > either the old bucket if it is not resized yet, or to the new
> > bucket if it has been resized, and \co{hashtab_del()} removes
> > the specified element from any buckets into which it has been inserted.
> > - \co{hashtab_lookup()} searches the new bucket if the search
> > - of the old bucket fails.
> > + The \co{hashtab_lookup()} function searches the new bucket
> > + if the search of the old bucket fails, which has the disadvantage
> > + of adding overhead to the lookup fastpath.
> > The alternative \co{hashtab_lock_mod()} returns the locking
> > state of the new bucket in \co{->hbp[0]} and \co{->hls_idx[0]}
> > - if resize operation is in progress.
> > - This reordering simplifies \co{hashtab_add()}, but at the expense
> > - of an extra check in \co{hashtab_lookup()}.
> > + if resize operation is in progress, instead of the perhaps
> > + more natural choice of \co{->hbp[1]} and \co{->hls_idx[1]}.
> > + However, this less-natural choice has the advantage of simplifying
> > + \co{hashtab_add()}.
> >
> > Further analysis of the code is left as an exercise for the reader.
> > } \QuickQuizEnd
> >
>
