Messages in this thread | | | Subject | Re: Softirq priority inversion from "softirq: reduce latencies" | From | Eric Dumazet <> | Date | Sat, 27 Feb 2016 17:59:26 -0800 |
| |
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@hurleysoftware.com> > > 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.
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.
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 ?
| |