> On Mon, Mar 18, 2019 at 12:09:32PM +0100, Lorenzo Bianconi wrote:
> > Similar to pci counterpart, reduce locking in mt76u_tx_tasklet since
> > q->head is managed just in mt76u_tx_tasklet and q->queued is updated
> > holding q->lock
> >
> > Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> > ---
> > drivers/net/wireless/mediatek/mt76/usb.c | 18 +++++++++++-------
> > 1 file changed, 11 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> > index ac03acdae279..8cd70c32d77a 100644
> > --- a/drivers/net/wireless/mediatek/mt76/usb.c
> > +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> > @@ -634,29 +634,33 @@ static void mt76u_tx_tasklet(unsigned long data)
> > int i;
> >
> > for (i = 0; i < IEEE80211_NUM_ACS; i++) {
> > + u32 n_queued = 0, n_sw_queued = 0;
> > +
> > sq = &dev->q_tx[i];
> > q = sq->q;
> >
> > - spin_lock_bh(&q->lock);
> > - while (true) {
> > + while (q->queued > n_queued) {
> > buf = &q->entry[q->head].ubuf;
> > - if (!buf->done || !q->queued)
> > + if (!buf->done)
> > break;
>
> I'm still thinking if this is safe or not. Is somewhat tricky to
> read variable outside the lock because in such case there is no time
> guarantee when variable written on one CPU gets updated value on
> different CPU. And for USB is not only q->queued but also buf->done.
Hi Stanislaw,
I was wondering if this is safe as well, but q->queued is updated holding q->lock
and I guess it will ensure to not overlap tx and status code path.
Regarding buf->done, it is already updated without holding the lock in mt76u_complete_tx
Regards,
Lorenzo
>
> Stanislaw
>
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