On Tue, 6 Oct 2015, Felipe Balbi wrote: > this commit causes a performance regression for the USB driver on > several platforms (anybody using drivers/usb/dwc3, basically). > > Here's the USB throughput with linux-next in 3 different scenarios: > > 1) Linux next without threadirqs cmdline > > test 0: sent 256.00 MB read 33.02 MB/s write 30.01 MB/s > > 2) Linux next with threadirqs on cmdline > > test 0: sent 256.00 MB read 30.70 MB/s write 27.89 MB/s > > 3) Linux next with threadirqs on cmdline + revert of $subject > > test 0: sent 256.00 MB read 32.93 MB/s write 29.85 MB/s > > > Considering this is trying to solve an issue found on the SDHCI driver, > shouldn't that be fixed instead ? Another option would be, of course, to > add IRQF_NO_THREAD to dwc3, but I'd like to avoid that if possible. It's not only an issue for SDHCI. It's a general problem with other drivers as well. > The way we try to use dwc3 is rather simple, actually. We use the > primary handle *only* to detect is $this device generated the IRQ and if > did we wake up the thread. We also don't make use of ONESHOT because we > mask $this device IRQs in the primary handler and only unmask after the > thread runs. So in your case IRQF_NO_THREAD is really the solution. It will keep your primary handler handled in the hard interrupt context. That will work on RT as well. > It's a bit surprising, to me at least, that simply running everything as > a thread would have such a measurable impact, but it does. I'm surprised of the size of the impact as well. I wouldn't have expected that another kernel thread context switch makes such a difference. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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