On Tue, 2015-06-02 at 12:08 -0600, Jason Gunthorpe wrote: > On Tue, Jun 02, 2015 at 10:35:24AM -0400, Doug Ledford wrote: > > > 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. > > No, if they followed (I didn't check yes) the extension scheme then the > poll call is > > struct ibv_wc_ex wcs[num_wcs] > ibv_poll_wc_ex(&wcs,num_wcs,sizeof(wcs[0])); > > And the drivers decide what to do based on the 3rd argument, which is > essentially the ABI version.
Ick. OK. I would *much* prefer something done akin to the routines in packer.c of the kernel, but that's not my call to make, the decision on the ABI/API extension mechanism was made long ago. It does, however, mean that extensions are serial and not modular, and that's a shame. > > 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? > > Not off hand, but that was different, that was a misuse of comp_mask, > IIRC. > > Or, the question in my mind based on looking at the UAPI patches is > what things should be driver private and what should be general. > > Broadly my thoughts: > - Should the frequency and mask be general, or driver private? If the > cycles->ns conversion is a function they should be driver private. > Even if they are general at libibverbs, they don't *have* to be in > the kernel's general query response. > - Should frequency even be frequency? Most clocks are expressed > accurately as a period in picoseconds. Frequency is more often > imprecise. (eg ethernet is 3200 ps or 312.5MHz) > However FDR/EDR is fractional for both (4693.33333333 ps vs > 213.0681818181818 MHz) > Precision is very important for time conversions, so a > multiply-divide scheme would be ideal. > This is suggesting to me these details really are not > general. > - There should be much better definition on what all this stuff is, > units for frequency? When is the timestamp applied? > - Should an app even be exposed to mask? This is very difficult > to use correctly in the general case. Only cases where an app is > restarted more often than a wrap period are trivial to use properly. > > Jason > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Doug Ledford <[email protected]> GPG KeyID: 0E572FDD
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