On Wed, Jul 06, 2022 at 11:09:43AM +0000, David Laight wrote: > From: Praveen Kumar > > Sent: 06 July 2022 10:15 > > > > On 05-07-2022 21:02, Saurabh Sengar wrote: > > > There can be scenarios where packets in ring buffer are continuously > > > getting queued from upper layer and dequeued from storvsc interrupt > > > handler, such scenarios can hold the foreach_vmbus_pkt loop (which is > > > executing as a tasklet) for a long duration. Theoretically its possible > > > that this loop executes forever. Add a condition to limit execution of > > > this tasklet for finite amount of time to avoid such hazardous scenarios. > > Does this really make much difference? > > I'd guess the tasklet gets immediately rescheduled as soon as > the upper layer queues another packet? > > Or do you get a different 'bug' where it is never woken again > because the ring is stuck full? > > David My initial understanding was that staying in a tasklet for "too long" may not be a good idea, however I was not sure what the "too long" value be, thus we are thinking to provide this parameter as a configurable sysfs entry. I couldn't find any linux doc justifying this, so please correct me here if I am mistaken. We have also considered the networking drivers NAPI budget feature while deciding this approach, where softirq exits once the budget is crossed. This budget feature act as a performance tuning parameter for driver, and also can help with ring buffer overflow. I believe similar reasons are true for scsi softirq as well. NAPI budget Ref : https://wiki.linuxfoundation.org/networking/napi. - Saurabh > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
