On Tue, Mar 21, 2017 at 12:01:58AM -0600, Alex Williamson wrote: >On Tue, 21 Mar 2017 16:43:05 +1100 >Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx> wrote: >> On Mon, Mar 20, 2017 at 10:57:08PM -0600, Alex Williamson wrote: >> >On Mon, 20 Mar 2017 18:34:23 -0500 >> >Bodong Wang <bodong@xxxxxxxxxxxx> wrote: >> >> .../... >> >> >> > Bodong, I'm not sure if there is a requirement to load driver for the >> >> > specified number of VFs? That indicates no driver will be loaded for >> >> > other VFs. If so, this interface might serve the purpose as well. >> >> Gavin, thanks for the review. That is indeed an interesting suggestion. >> >> Theoretically, we can change that probe_vfs from boolean to integer. >> >> And use it as a counter to probe the first N VFs(if N < total_vfs). >> >> Let's see if there are any objections. >> > >> >Is it just me or does this seem like a confusing user interface, ie. to >> >get binary on/off behavior a user now needs to 'cat total_vfs > >> >sriov_probe_vfs'. It's not very intuitive, what's the use case for it? >> > >> >> After it's changed to integer, it accepts number. If users want to load >> driver for all VFs and don't want to check the maximal number of VFs, >> they can simply write 0xffffffff. So "on" and "off" are replaced with 0xffffffff >> and 0, but users has to press the keyboard more times though. >> >> drivers/net/ethernet/mellanox/mlx4/main.c::probe_vfs_argc allows to specify >> the number of VFs with which we're going to bind drivers. Less time is needed >> to enable SRIOV capability. As I had in some development environment: assume >> PF supports 256 VFs and I'm going to enable all of them, but I only want to >> load driver for two of them, then test the data path on those two VFs. Besides, >> I can image the VF needn't a driver in host if it's going to be passed to guest. >> Not sure how much sense it makes. > >Yes, I understand what you're trying to do, but I still think it's >confusing for a user interface. This also doesn't answer what's the >practical, typical user case you see where it's useful to probe some >VFs but not others. The case listed is a development case where you >could just as easily disable all probing, then manually bind the first >two VFs to the host driver. Which is the better design, impose a >confusing interface on all users to simplify an obscure development >environment or simplify the user interface and assume developers know >how to bind devices otherwise? Thanks, > Yeah, your explanation is also fairly reasonable. The interface has been named as "probe_vfs" instead of "probe_vf" or "probe_vf_driver". So it seems it should accept number of VFs on which drivers are loaded. Besides, making this interface accept number corresponds to 3 possiblities: all, none and load drivers on part of available VFs. So more flexibility is gained. User can theoritically have the use case as I had - passing through some of the VFs to guest: (A) All VFs are bound with drivers; (B) unbind the drivers for some of the VFs; (C) bind the VFs with vfio-pci; (D) passing through; (A) is overhead in this scenario. Some CPU cycles are saved if (A) is avoided. Thanks, Gavin
