From: Yang Yingliang <yangyingliang@huawei•com>
To: David Laight <David.Laight@ACULAB•COM>, <davem@davemloft•net>,
<netdev@vger•kernel.org>
Cc: <eric.dumazet@gmail•com>, <brouer@redhat•com>,
<jpirko@redhat•com>, <jbrouer@redhat•com>
Subject: Re: [PATCH net v6 1/2] net: sched: tbf: fix the calculation of max_size
Date: Mon, 9 Dec 2013 11:26:02 +0800 [thread overview]
Message-ID: <52A5384A.8050106@huawei.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B7468@saturn3.aculab.com>
On 2013/12/6 18:56, David Laight wrote:
>> From: Yang Yingliang
> ...
>>
>> +/* Time to Length, convert time in ns to length in bytes
>> + * to determinate how many bytes can be sent in given time.
>> + */
>> +static u64 psched_ns_t2l(const struct psched_ratecfg *r,
>> + u64 time_in_ns)
>> +{
>> + /* The formula is :
>> + * len = (time_in_ns * r->rate_bytes_ps) / NSEC_PER_SEC
>> + */
>> + u64 len = time_in_ns * r->rate_bytes_ps;
>> +
>> + do_div(len, NSEC_PER_SEC);
>
> You are multiplying two values then dividing by 10**9
> I'd guess that the intermediate value might exceed 2**64.
>
>> + if (unlikely(r->linklayer == TC_LINKLAYER_ATM))
>> + len = (len / 53) * 48;
>
> You probably want to do the multiply first.
> But why not scale rate_bytes_ps instead.
>
When the linklayer is ATM, the formula to calculate tokens is:
((u64)(DIV_ROUND_UP(len,48)*53) * r->mult) >> r->shift
So, I scale len here.
Regards,
Yang
next prev parent reply other threads:[~2013-12-09 3:26 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-06 7:00 [PATCH net v6 0/2] net: sched: fix two issues Yang Yingliang
2013-12-06 7:00 ` [PATCH net v6 1/2] net: sched: tbf: fix the calculation of max_size Yang Yingliang
2013-12-06 10:56 ` David Laight
2013-12-09 2:26 ` Yang Yingliang
2013-12-09 3:26 ` Yang Yingliang [this message]
2013-12-09 10:07 ` David Laight
2013-12-09 12:21 ` Yang Yingliang
2013-12-09 13:10 ` [PATCH RFC ] " Yang Yingliang
2013-12-09 15:12 ` Eric Dumazet
2013-12-10 2:29 ` Yang Yingliang
2013-12-10 2:39 ` Eric Dumazet
2013-12-09 13:11 ` [PATCH net v6 1/2] " David Laight
2013-12-10 2:04 ` Yang Yingliang
2013-12-06 7:00 ` [PATCH net v6 2/2] net: sched: htb: fix the calculation of quantum Yang Yingliang
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=52A5384A.8050106@huawei.com \
--to=yangyingliang@huawei$(echo .)com \
--cc=David.Laight@ACULAB$(echo .)COM \
--cc=brouer@redhat$(echo .)com \
--cc=davem@davemloft$(echo .)net \
--cc=eric.dumazet@gmail$(echo .)com \
--cc=jbrouer@redhat$(echo .)com \
--cc=jpirko@redhat$(echo .)com \
--cc=netdev@vger$(echo .)kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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