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!
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
>
