From: 康宁 <kangning18z@ict.ac.cn>
To: "Leon Romanovsky" <leon@kernel.org>
Cc: haakon.bugge@oracle.com, linux-rdma@vger.kernel.org
Subject: Re: Re: [PATCH v3] Fix one error in mthca_alloc
Date: Tue, 31 Aug 2021 18:40:38 +0800 (GMT+08:00) [thread overview]
Message-ID: <30f8792b.1e35e.17b9bcbf058.Coremail.kangning18z@ict.ac.cn> (raw)
In-Reply-To: <YS371Qgef1FTTrHZ@unreal>
>
> On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote:
> > drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which
> > has impact on performance of function find_next_zero_bit in mthca_alloc.
>
> I don't know what the sentence above means, but the change is unlikely
> to be correct.
>
> When alloc->last starts to be equal to alloc->max, the
> find_next_zero_bit() will always return alloc->max. which will ensure
> that the following code is executed.
>
> 48 if (obj >= alloc->max) {
> 49 alloc->top = (alloc->top + alloc->max) & alloc->mask;
> 50 obj = find_first_zero_bit(alloc->table, alloc->max);
> 51 }
>
Thanks for your review.
Yes, your analysis is right. However, this is a bitmap allocator for resource id allocation (like QP, and CQ).
We first look at the situation where no resource id is released.
When the value of alloc->last starts to reaches alloc->max, the bitmap will
be full. In this case, it's normal to return an invalid value.
Now, let's add resource releasing into consideration.
The following code is part of mthca_free:
70 spin_lock_irqsave(&alloc->lock, flags);
71
72 clear_bit(obj, alloc->table);
73 alloc->last = min(alloc->last, obj);
74 alloc->top = (alloc->top + alloc->max) & alloc->mask;
mthca_free() is used to release the allocated resource id. It will update alloc->last when obj is freed.
So, if the bitmap has space for allocation, my modification can continuously work.
>
> However the mthca_alloc() function has other error, it returns -1 while
> based on its declaration it needs to be unsigned,
I think you are right about this. But obj is the return value of u32 type, which is the requirement of resource id
(though it may not fully use 32 bits). I have no idea of how to fix it.
Thanks.
>
> Thanks
>
> >
> > Signed-off-by: kangning <kangning18z@ict.ac.cn>
> > ---
> >
> > I squashed two commits into one in this version.
> >
> > drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c
> > index aef1d274a14e..1141695093e7 100644
> > --- a/drivers/infiniband/hw/mthca/mthca_allocator.c
> > +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c
> > @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc)
> > }
> >
> > if (obj < alloc->max) {
> > + alloc->last = obj + 1;
> > + if (alloc->last == alloc->max)
> > + alloc->last = 0;
> > set_bit(obj, alloc->table);
> > obj |= alloc->top;
> > } else
> > --
> > 2.17.1
> >
</kangning18z@ict.ac.cn>
next prev parent reply other threads:[~2021-08-31 10:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 0:52 [PATCH v3] Fix one error in mthca_alloc kangning
2021-08-31 9:52 ` Leon Romanovsky
2021-08-31 10:40 ` 康宁 [this message]
2021-08-31 12:00 ` Leon Romanovsky
2021-08-31 12:16 ` kangning18z
2021-08-31 10:47 ` 康宁
[not found] ` <202109011027459851120@ict.ac.cn>
2021-09-01 7:51 ` Leon Romanovsky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=30f8792b.1e35e.17b9bcbf058.Coremail.kangning18z@ict.ac.cn \
--to=kangning18z@ict.ac.cn \
--cc=haakon.bugge@oracle.com \
--cc=leon@kernel.org \
--cc=linux-rdma@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).