From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> When writing data we were: lock do some work unlock call function lock do some work unlock return return It turns out, that "function" was only ever called in the one place, so instead of locking/unlocking for no good reason, just inline the function and only grab the lock once. This has sped up the pathological case of sending 1 byte packets to a loop-back cdc-acm device from 49600 bytes per second to 50100 bytes a second on my workstation. A tiny increase yes, but noticable, and now the spinlock isn't the hottest thing on the perf graph anymore. Yes, we are still waiting for the hardware for the most part, but getting rid of a spinlock_irq_save() call for every packet is still a good thing. And we end up deleting lines of code, always a win overall. This was found by using a Teensy 3.0 device and the test program and firmware located at: http://www.pjrc.com/teensy/benchmark_usb_serial_receive.html Reported-by: Paul Stoffregen <paul@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- Changes v1 - v2: - move unlock farther down the call to where it needed to be. drivers/usb/class/cdc-acm.c | 52 ++++++++++++++++---------------------------- 1 file changed, 19 insertions(+), 33 deletions(-) --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -216,38 +216,6 @@ static int acm_start_wb(struct acm *acm, return rc; } -static int acm_write_start(struct acm *acm, int wbn) -{ - unsigned long flags; - struct acm_wb *wb = &acm->wb[wbn]; - int rc; - - spin_lock_irqsave(&acm->write_lock, flags); - if (!acm->dev) { - wb->use = 0; - spin_unlock_irqrestore(&acm->write_lock, flags); - return -ENODEV; - } - - dev_vdbg(&acm->data->dev, "%s - susp_count %d\n", __func__, - acm->susp_count); - usb_autopm_get_interface_async(acm->control); - if (acm->susp_count) { - if (!acm->delayed_wb) - acm->delayed_wb = wb; - else - usb_autopm_put_interface_async(acm->control); - spin_unlock_irqrestore(&acm->write_lock, flags); - return 0; /* A white lie */ - } - usb_mark_last_busy(acm->dev); - - rc = acm_start_wb(acm, wb); - spin_unlock_irqrestore(&acm->write_lock, flags); - - return rc; - -} /* * attributes exported through sysfs */ @@ -653,13 +621,31 @@ static int acm_tty_write(struct tty_stru } wb = &acm->wb[wbn]; + if (!acm->dev) { + wb->use = 0; + spin_unlock_irqrestore(&acm->write_lock, flags); + return -ENODEV; + } + count = (count > acm->writesize) ? acm->writesize : count; dev_vdbg(&acm->data->dev, "%s - write %d\n", __func__, count); memcpy(wb->buf, buf, count); wb->len = count; + + usb_autopm_get_interface_async(acm->control); + if (acm->susp_count) { + if (!acm->delayed_wb) + acm->delayed_wb = wb; + else + usb_autopm_put_interface_async(acm->control); + spin_unlock_irqrestore(&acm->write_lock, flags); + return count; /* A white lie */ + } + usb_mark_last_busy(acm->dev); + + stat = acm_start_wb(acm, wb); spin_unlock_irqrestore(&acm->write_lock, flags); - stat = acm_write_start(acm, wbn); if (stat < 0) return stat; return count; -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
