[dpdk-dev] 答复: [PATCH] Add user defined tag calculation callback tolibrte_distributor.
jigsaw at gmail.com
Thu Nov 6 20:52:25 CET 2014
Actually IMHO it is good to leave the freedom to user to decide how to
interpret the tag value, i.e. remove the OR 1 bit.
If the tag value is zero, then we assume the programmer know what he is
doing. Of course this shall be clearly documented in the comment/doxgen.
On Thu, Nov 6, 2014 at 8:01 PM, jigsaw <jigsaw at gmail.com> wrote:
> Hi Bruce,
> In my use case, unfortunately the tag is not hash. And the tag can be on
> either low or high bits, depending on configuration.
> I wonder if it is possible to let the user to decide which bit to mask,
> i.e. to add another param to rte_distributor_create to define the mask.
> thx &
> On Thu, Nov 6, 2014 at 3:59 PM, Bruce Richardson <
> bruce.richardson at intel.com> wrote:
>> On Thu, Nov 06, 2014 at 02:36:09PM +0200, Qinglai Xiao wrote:
>> > Hi Bruce,
>> > There is a subtle case in which tag values are 2 and 3, respectively.
>> Then these two tags cannot be distinguished. There should be a better way
>> so as to handle this situation.
>> It's not just in that, case, it's in any case where a pair of tags differ
>> only a single bit. I've been assuming that the tag is likely to be a hash
>> value in most cases - given that it's only 32-bit - in which case it just
>> matter which bit we chose to permanently set to 1, but if there are
>> where it's likely that the low bits are used but the high ones not so, we
>> look to change which bit is set to 1. Either way, the distributor just
>> uses a
>> 31-bit tag rather than a 32-bit one.
>> > thx &
>> > rgds
>> > -qinglai
>> > -----原始邮件-----
>> > 发件人: "Thomas Monjalon" <thomas.monjalon at 6wind.com>
>> > 发送时间: 2014/11/6 12:36
>> > 收件人: "Bruce Richardson" <bruce.richardson at intel.com>
>> > 抄送: "dev at dpdk.org" <dev at dpdk.org>; "jigsaw" <jigsaw at gmail.com>
>> > 主题: Re: [dpdk-dev] [PATCH] Add user defined tag calculation callback
>> > 2014-11-06 09:22, Bruce Richardson:
>> > > On Wed, Nov 05, 2014 at 07:24:13PM +0200, jigsaw wrote:
>> > > >
>> > > >
>> > > > new_tag = (next_mb->hash.rss | 1);
>> > > >
>> > > > Why the logical OR is needed?
>> > >
>> > > That's needed to ensure that we never track a tag with an actual
>> value of zero.
>> > > We instead always force the low bit to be 1, so that we can use zero
>> as an
>> > > "empty" value.
>> > Bruce, could you check how this code may be better commented please?
>> > This discussion shows that the distributor library probably needs more
>> > explanations in the code or doxygen.
>> > Thanks
>> > --
>> > Thomas
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