[ovs-dev] [PATCH v2 7/7] flow: Add struct flowmap.

Jarno Rajahalme jrajahalme at nicira.com
Sat Aug 8 00:00:24 UTC 2015


> On Aug 6, 2015, at 5:39 PM, Jarno Rajahalme <jrajahalme at nicira.com> wrote:
> 
>> On Aug 6, 2015, at 16:29, Jesse Gross <jesse at nicira.com> wrote:
> 
>> 
>>> On Thu, Aug 6, 2015 at 4:17 PM, Jarno Rajahalme <jrajahalme at nicira.com> wrote:
>>> Struct miniflow is now sometimes used just as a map.  Define a new
>>> struct flowmap for that purpose.  The flowmap is defined as an array of
>>> maps, and it is automatically sized according to the size of struct
>>> flow, so it will be easier to maintain in the future.
>>> 
>>> It would have been tempting to use the existing struct bitmap for this
>>> purpose. The main reason this is not feasible at the moment is that
>>> some flowmap algorithms are simpler when it can be assumed that no
>>> struct flow member requires more bits than can fit to a single map
>>> unit. The tunnel member already requires more than 32 bits, so the map
>>> unit needs to be 64 bits wide.
>>> 
>>> Performance critical algorithms enumerate the flowmap array units
>>> explicitly, as it is easier for the compiler to optimize, compared to
>>> the normal iterator.  Without this optimization a classifier lookup
>>> without wildcard masks would be about 25% slower.
>>> 
>>> With this more general (and maintainable) algorithm the classifier
>>> lookups are about 5% slower, when the struct flow actually becomes big
>>> enough to require a second map.  This negates the performance gained
>>> in the "Pre-compute stage masks" patch earlier in the series.
>>> 
>>> Requested-by: Ben Pfaff <blp at nicira.com>
>>> Signed-off-by: Jarno Rajahalme <jrajahalme at nicira.com>
>> 
>> I think this patch may need a rebase after the tunnel metadata flow
>> patches that I applied last night.
>> 
>> Sorry about that.
> 
> Thanks for the heads up! I just sent a v3.
> 

I did some more testing and profiling and sent an improved version (v4). No changes in the first few patches.

  Jarno




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