On Tue, Mar 21, 2017 at 08:23:29AM -0600, Alex Williamson wrote: >On Tue, 21 Mar 2017 20:25:18 +1100 >Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx> wrote: >> 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. > >Huh? I'm asking what the practical and typical use case is for this >and you're rehashing the name of the interface and giving me >theoretical examples. Outside of your development environment, why >would a user every actually want to do this? > Frankly, I'm not sure how much sense it has as I mentioned from the beginning. I knew mlx4 driver supports it and it's why I asked. >If we want to talk about the ABI, I would suggest drawing from existing >ABIs. We already have drivers_autoprobe as part of the standard sysfs >ABI, so if we want a binary switch, then sriov_drivers_autoprobe might >be a logical choice. If you're concerned about this mythical overhead >of binding to one driver then another, then why not draw from the >driver_override interface to allow the user to specify the driver to >bind to, perhaps sriov_driver_override. Then if the user wants to bind >all the devices to vfio-pci, they can do so easily. I still fail to >see that probing some fixed number of the VFs and leaving the rest >unprobed has any practical value and I imagine bugs coming in because >users are confused why some of their VFs behave differently than >others. Thanks, > Ok. I tend to agree with you - the use case isn't practical. On the other hand, I think "sriov_driver_orverride" would be a good idea, but it's not too much related to this patch. Thank you for the explanation. Thanks, Gavin
