Hi Dominique, On 2018/7/18 17:54, Dominique Martinet wrote: > piaojun wrote on Wed, Jul 18, 2018: >> spin_lock is more effective for short time protection than mutex_lock, as >> mutex lock may cause process sleep and wake up which consume much cpu >> time. > > That's not a fast path operation, I don't mind changing things but I'd > like to understand why - these functions are only ever called at unmount > time or when something happens on the virtio bus (probe will happen on > probing on the pci bus and I'm not too sure on remove but probably pci > removal i.e. basically never?) > > I don't see why this wouldn't work, but I won't take this without a > (good?) reason. > virtio_9p_lock is responsable for protecting virtio_chan_list which has 3 operation:
1. Add a virtio chan to virtio_chan_list. This will happen when we insmod 9pnet_virtio.ko: p9_virtio_probe --list_add_tail(&chan->chan_list, &virtio_chan_list); 2. Remove a virtio chan. This will happen when remnod 9pnet_virtio.ko: p9_virtio_remove --list_del(&chan->chan_list); 3. Find a unused virtio chan when mount 9p: mount --p9_virtio_create --list_for_each_entry(chan, &virtio_chan_list, chan_list) Multi mount process will compete for virtio_9p_lock when finding unused virtio chan, in which case mutex lock will cause process sleep and wake up. I think this a waste of CPU time. So we could use spin lock to avoid this. Thanks, Jun
