On Tue, 2015-06-02 at 17:44 +0300, Or Gerlitz wrote: > On 6/2/2015 5:35 PM, Doug Ledford wrote: > > On Mon, 2015-06-01 at 10:43 -0600, Jason Gunthorpe wrote: > >> On Mon, Jun 01, 2015 at 07:25:04AM -0400, Doug Ledford wrote: > >> > >>> attempted abstraction of ibverbs. Passing in the wc struct allows the > >>> driver to internally allocate a wc struct with extra private elements > >>> and pass that back to the user, when the user passes it back to > >>> ibv_get_timestamp the elements are there in the private portion of the > >>> struct. > >> wc structures are allocated by the caller, there is no option for the > >> driver to create private elements. > > Well, they *are* using an extended work completion structure. Unlike > > what I mentioned, where they create a larger one themselves, you have to > > allocate a struct ibv_wc_ex instead of a struct ibv_wc and then you have > > to call poll_cq_ex, which expects a struct ibv_wc_ex. > > > > So, just so everyone is clear on this point: the current user space > > implementation of this feature creates an unversioned, newly named > > ibv_wc_ex struct that is ibv_wc with a 64bit timestamp tacked on at the > > end (not 64bit aligned either). If we ever wanted to have a different > > extension to our ibv_wc struct, there is no good way to do that. If, at > > some point, we had multiple extension and the user was able to select > > which they wanted to utilize, this structure extension is not flexible > > enough to deal with that. At a minimum, if we are going to have a one > > shot extension to the wc struct like this, I would prefer to see it > > called struct ibv_wc_timestamp and there be a ibv_poll_cq_timestamp. At > > least that way people would not use the generic _ex and assume this is > > the one and only _ex that we will ever need for work completions. > > > > Jason, when the XRC and flow steering extensions were added to > > libibverbs, you complained loudly that they were not added in the agreed > > upon format and cited a previous on list discussion. Do you have a link > > to that discussion? > > Doug, > > Do we agree that this part of the discussion (and also the below point) > are related to the libibverbs API to applications and not to the kernel > -> user API to support time-stamping? Yes. > Or. > > > > >> AFAIK, Christoph's use case is essentially the only meaningful use > >> case for this feature, generalizing too much may destroy the > >> performance that is valuable here. > > There is actually room in a 64byte cacheline for two 64bit timestamps > > and another 2 bytes of padding or something else. > > > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Doug Ledford <dledford@xxxxxxxxxx> GPG KeyID: 0E572FDD
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