[ovs-dev] [PATCH RFC 0/1] dpif-netdev: Make EMC Size Configurable

[Pravin Shelar]

On Tue, Apr 21, 2015 at 6:33 PM, Ethan Jackson <ethan at nicira.com> wrote:
> I really don't think this should be configurable, I can't imagine a
> situation in which a user would have enough knowledge to tweak the
> knob correctly.  I think the only reason we'd want to configure it is
> the current EMC size is too small at the moment.  My preference would
> be to figure out how to make it bigger, i.e. by doing prefetching and
> what not.
>

It does depends on amount of memory available in system which can vary
alot in practice. If you have lot of memory and few devices user can
configure bigger EMC accordingly. Thats why it could be useful to make
it configurable at vswitchd startup time.

> Ethan
>
> On Tue, Apr 21, 2015 at 5:49 PM, Pravin Shelar <pshelar at nicira.com> wrote:
>> On Tue, Apr 21, 2015 at 9:01 AM, Loftus, Ciara <ciara.loftus at intel.com> wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Ben Pfaff [mailto:blp at nicira.com]
>>>> Sent: Tuesday, April 21, 2015 4:08 PM
>>>> To: Loftus, Ciara
>>>> Cc: dev at openvswitch.org
>>>> Subject: Re: [ovs-dev] [PATCH RFC 0/1] dpif-netdev: Make EMC Size
>>>> Configurable
>>>>
>>>> On Tue, Apr 21, 2015 at 01:47:12PM +0100, Ciara Loftus wrote:
>>>> > This patch allows the user to specify the number of Exact Match Cache
>>>> > entries they wish to have available for their instance of the vswitch.
>>>> > This is a achieved by means of a 'configure' flag.
>>>> >
>>>> > At the moment, the default number of EMC entries is 1024, for which
>>>> > the switch should perform optimally up to this number of flows.
>>>> > However, if the user expects say roughly 2000 flows of traffic, an EMC
>>>> > with 2048 entries will perform better, allbeit with a larger demand on
>>>> > memory and time spent flushing the cache. If these requirements are
>>>> > acceptable to the user, they may choose to allocate 2048 entries like so,
>>>> > and in turn receive improved performance for their specific use case:
>>>> >
>>>> > './configure --with-emcsize=11'
>>>> >
>>>> > The number of entries is calculated as 2^11 = 2048.
>>>>
>>>> configure flags are really inconvenient.  Is there a reason that this
>>>> can't be made configurable at runtime?  It would be better yet if the
>>>> EMC size could automatically adjust itself.
>>>
>>> Thanks for the feedback. The implementation is naturally more complex for a runtime configurable but I think achievable - I'll look into it.
>>>
>> It should be easier to have a ovs-vswitchd command-line argument to
>> make the size configurable.
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