| Message ID | 20210608085438.813960-1-zenczykowski@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 1958ff5ad2d4908b44a72bcf564dfe67c981e7fe |
| Headers | show |
| Series | usb: f_ncm: only first packet of aggregate needs to start timer | expand |
On Tue, Jun 08, 2021 at 01:54:38AM -0700, Maciej Żenczykowski wrote: > From: Maciej Żenczykowski <maze@google.com> > > The reasoning for this change is that if we already had > a packet pending, then we also already had a pending timer, > and as such there is no need to reschedule it. > > This also prevents packets getting delayed 60 ms worst case > under a tiny packet every 290us transmit load, by keeping the > timeout always relative to the first queued up packet. > (300us delay * 16KB max aggregation / 80 byte packet =~ 60 ms) > > As such the first packet is now at most delayed by 300us. > > Under low transmit load, this will simply result in us sending > a shorter aggregate, as originally intended. > > This patch has the benefit of greatly reducing (by ~10 factor > with 1500 byte frames aggregated into 16 kiB) the number of > (potentially pretty costly) updates to the hrtimer. > > Cc: Brooke Basile <brookebasile@gmail.com> > Cc: Bryan O'Donoghue <bryan.odonoghue@linaro.org> > Cc: Felipe Balbi <balbi@kernel.org> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Lorenzo Colitti <lorenzo@google.com> > Signed-off-by: Maciej Żenczykowski <maze@google.com> > --- > drivers/usb/gadget/function/f_ncm.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c > index 0d23c6c11a13..855127249f24 100644 > --- a/drivers/usb/gadget/function/f_ncm.c > +++ b/drivers/usb/gadget/function/f_ncm.c > @@ -1101,11 +1101,11 @@ static struct sk_buff *ncm_wrap_ntb(struct gether *port, > ncm->ndp_dgram_count = 1; > > /* Note: we skip opts->next_ndp_index */ > - } > > - /* Delay the timer. */ > - hrtimer_start(&ncm->task_timer, TX_TIMEOUT_NSECS, > - HRTIMER_MODE_REL_SOFT); > + /* Start the timer. */ > + hrtimer_start(&ncm->task_timer, TX_TIMEOUT_NSECS, > + HRTIMER_MODE_REL_SOFT); > + } > > /* Add the datagram position entries */ > ntb_ndp = skb_put_zero(ncm->skb_tx_ndp, dgram_idx_len); Nice, hopefully this helps out a lot on the systems where re-arming timers are slow. greg k-h
On Wed, Jun 09, 2021 at 10:27:48AM +0200, Greg Kroah-Hartman wrote: > On Tue, Jun 08, 2021 at 01:54:38AM -0700, Maciej Żenczykowski wrote: > > From: Maciej Żenczykowski <maze@google.com> > > > > The reasoning for this change is that if we already had > > a packet pending, then we also already had a pending timer, > > and as such there is no need to reschedule it. > > > > This also prevents packets getting delayed 60 ms worst case > > under a tiny packet every 290us transmit load, by keeping the > > timeout always relative to the first queued up packet. > > (300us delay * 16KB max aggregation / 80 byte packet =~ 60 ms) > > > > As such the first packet is now at most delayed by 300us. > > > > Under low transmit load, this will simply result in us sending > > a shorter aggregate, as originally intended. > > > > This patch has the benefit of greatly reducing (by ~10 factor > > with 1500 byte frames aggregated into 16 kiB) the number of > > (potentially pretty costly) updates to the hrtimer. > > > > Cc: Brooke Basile <brookebasile@gmail.com> > > Cc: Bryan O'Donoghue <bryan.odonoghue@linaro.org> > > Cc: Felipe Balbi <balbi@kernel.org> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > Cc: Lorenzo Colitti <lorenzo@google.com> > > Signed-off-by: Maciej Żenczykowski <maze@google.com> > > --- > > drivers/usb/gadget/function/f_ncm.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c > > index 0d23c6c11a13..855127249f24 100644 > > --- a/drivers/usb/gadget/function/f_ncm.c > > +++ b/drivers/usb/gadget/function/f_ncm.c > > @@ -1101,11 +1101,11 @@ static struct sk_buff *ncm_wrap_ntb(struct gether *port, > > ncm->ndp_dgram_count = 1; > > > > /* Note: we skip opts->next_ndp_index */ > > - } > > > > - /* Delay the timer. */ > > - hrtimer_start(&ncm->task_timer, TX_TIMEOUT_NSECS, > > - HRTIMER_MODE_REL_SOFT); > > + /* Start the timer. */ > > + hrtimer_start(&ncm->task_timer, TX_TIMEOUT_NSECS, > > + HRTIMER_MODE_REL_SOFT); > > + } > > > > /* Add the datagram position entries */ > > ntb_ndp = skb_put_zero(ncm->skb_tx_ndp, dgram_idx_len); > > Nice, hopefully this helps out a lot on the systems where re-arming > timers are slow. And that's what the changelog said, I need more coffee...
diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c index 0d23c6c11a13..855127249f24 100644 --- a/drivers/usb/gadget/function/f_ncm.c +++ b/drivers/usb/gadget/function/f_ncm.c @@ -1101,11 +1101,11 @@ static struct sk_buff *ncm_wrap_ntb(struct gether *port, ncm->ndp_dgram_count = 1; /* Note: we skip opts->next_ndp_index */ - } - /* Delay the timer. */ - hrtimer_start(&ncm->task_timer, TX_TIMEOUT_NSECS, - HRTIMER_MODE_REL_SOFT); + /* Start the timer. */ + hrtimer_start(&ncm->task_timer, TX_TIMEOUT_NSECS, + HRTIMER_MODE_REL_SOFT); + } /* Add the datagram position entries */ ntb_ndp = skb_put_zero(ncm->skb_tx_ndp, dgram_idx_len);