On 02/27/2016 05:59 PM, Eric Dumazet wrote: > On sam., 2016-02-27 at 15:33 -0800, Peter Hurley wrote: >> On 02/27/2016 03:04 PM, David Miller wrote: >>> From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> >>> Date: Sat, 27 Feb 2016 12:29:39 -0800 >>> >>>> Not really. softirq raised from interrupt context will always execute >>>> on this cpu and not in ksoftirqd, unless load forces softirq loop abort. >>> >>> That guarantee never was specified. >> >> ?? >> >> Neither is running network socket servers at normal priority as if they're >> higher priority than softirq. >> >> >>> Or are you saying that by design, on a system under load, your UART >>> will not function properly? >>> >>> Surely you don't mean that. >> >> No, that's not what I mean. >> >> What I mean is that bypassing the entire SOFTIRQ priority so that >> sshd can process one network packet makes a mockery of the point of softirq. >> >> This hack to workaround NET_RX looping over-and-over-and-over affects every >> subsystem, not just one uart. >> >> HI, TIMER, BLOCK; all of these are skipped: that's straight-up, a bug. > > No idea what you talk about. > > All pending softirq interrupts are processed. _Nothing_ is skipped. An interrupt that schedules HI softirq while in NET_RX softirq should still run the HI softirq. But with your patch that won't happen. > Really, your system stability seems to depend on a completely > undocumented behavior of linux kernels before linux-3.8 > > If I understood, you expect that a tasklet activated from a softirq > handler is run from the same __do_softirq() loop. This never has been > the case. No. The *interrupt handler* for DMA goes off while NET_RX softirq is running. That's what schedules the *DMA tasklet*. That tasklet should run before any process. But it doesn't because your patch bails out early from softirq. > My change simply triggers the bug in your driver earlier. As David > pointed out, your bug should trigger the same on a loaded machine, even > if you revert my patch. > > I honestly do not know why you arm a tasklet from NET_RX, why don't you > simply process this directly, so that you do not rely on some scheduler > decision ? -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
