[openib-general] SA cache design

[Hal Rosenstock]

Hi Sean,

On Tue, 2006-01-03 at 19:42, Sean Hefty wrote:
> I've been given the task of trying to come up with an implementation for an SA 
> cache.  The intent is to increase the scalability and performance of the openib 
> stack.  My current thoughts on the implementation are below.  Any feedback is 
> welcome.
> 
> To keep the design as flexible as possible, my plan is to implement the cache in 
> userspace.  The interface to the cache would be via MADs.

Would this be another MAD class which mimics the SA class ?

>   Clients would send 
> their queries to the sa_cache instead of the SA itself.  The format of the MADs 
> would be essentially identical to those used to query the SA itself.  Response 
> MADs would contain any requested information.  If the cache could not satisfy a 
> request, the sa_cache would query the SA, update its cache, then return a reply.
> 
> The benefits that I see with this approach are:
> 
> + Clients would only need to send requests to the sa_cache.
> + The sa_cache can be implemented in stages.  Requests that it cannot handle 
> would just be forwarded to the SA.

Another option would be for the SA cache to indicate what requests its
handles (some MADs for this) and have the clients only go to the cache
for those queries (and direct to the SA for the others).

> + The sa_cache could be implemented on each host, or a select number of hosts.
> + The interface to the sa_cache is similar to that used by the SA.
> + The cache would use virtual memory and could be saved to disk.
> 
> Some drawbacks specific to this method are:
> 
> - The MAD interface will result in additional data copies and userspace to 
> kernel transitions for clients residing on the local system.
> - Clients require a mechanism to locate the sa_cache, or need to make 
> assumptions about its location.

Would SA caching be a service ID or set of IDs ?

Are there also issues around cache invalidation ?

-- Hal