On Sun, Feb 18, 2024 at 08:11:58AM +0100, Greg KH wrote: > On Sat, Feb 17, 2024 at 10:03:35AM -0800, Saurabh Sengar wrote: > > Add a function to query for the preferred ring buffer size of VMBus > > device. > > That says what you did, but not why you did it. I thought subsequent patch will make it clear, but I can add more info in cover letter. I will enhance this commit as well. > > > > > Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> > > --- > > drivers/hv/channel_mgmt.c | 7 +++++-- > > drivers/hv/hyperv_vmbus.h | 5 +++++ > > include/linux/hyperv.h | 1 + > > 3 files changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c > > index 2f4d09ce027a..7ea444d72f9f 100644 > > --- a/drivers/hv/channel_mgmt.c > > +++ b/drivers/hv/channel_mgmt.c > > @@ -120,7 +120,8 @@ const struct vmbus_device vmbus_devs[] = { > > }, > > > > /* File copy */ > > - { .dev_type = HV_FCOPY, > > + { .pref_ring_size = 0x4000, > > + .dev_type = HV_FCOPY, > > HV_FCOPY_GUID, > > .perf_device = false, > > .allowed_in_isolated = false, > > @@ -141,11 +142,13 @@ const struct vmbus_device vmbus_devs[] = { > > }, > > > > /* Unknown GUID */ > > - { .dev_type = HV_UNKNOWN, > > + { .pref_ring_size = 0x11000, > > + .dev_type = HV_UNKNOWN, > > Where do these magic numbers for the size come from? This value is (16 + 1) page_size, which is found sufficient for most of the slow devices. 16 page_size is for the ringbuffer and 1 page_size for the headre. This is the approximation for default case, to avoid using fall back case of 512 page_size as used by uio_hv_generic. > > > .perf_device = false, > > .allowed_in_isolated = false,> > }, > > }; > > +EXPORT_SYMBOL_GPL(vmbus_devs); > > > > static const struct { > > guid_t guid; > > diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h > > index f6b1e710f805..76ac5185a01a 100644 > > --- a/drivers/hv/hyperv_vmbus.h > > +++ b/drivers/hv/hyperv_vmbus.h > > @@ -417,6 +417,11 @@ static inline bool hv_is_perf_channel(struct vmbus_channel *channel) > > return vmbus_devs[channel->device_id].perf_device; > > } > > > > +static inline size_t hv_dev_ring_size(struct vmbus_channel *channel) > > +{ > > + return vmbus_devs[channel->device_id].pref_ring_size; > > +} > > + > > static inline bool hv_is_allocated_cpu(unsigned int cpu) > > { > > struct vmbus_channel *channel, *sc; > > diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h > > index 2b00faf98017..5951c7bb5712 100644 > > --- a/include/linux/hyperv.h > > +++ b/include/linux/hyperv.h > > @@ -800,6 +800,7 @@ struct vmbus_requestor { > > #define VMBUS_RQST_RESET (U64_MAX - 3) > > > > struct vmbus_device { > > + size_t pref_ring_size; > > No documentation for this? What is the size in units of? I can add a comment here like below: /* * Total memory in bytes allocated for the one complete ring buffer, * which includes the ring buffer header, of size PAGE_SIZE. This value * should be aligned to page_size. */ - Saurabh > > thanks, > > greg k-h