Hi, Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes: > 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. all right. I'll patch that up. Thanks -- balbi
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