On Thu, May 27, 2021 at 09:06:04AM -0400, Nitesh Lal wrote: > On Thu, May 27, 2021 at 6:03 AM Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx> wrote: > > > > Hi, > > > > On Fri, May 21, 2021 at 02:03:06PM +0200, Thomas Gleixner wrote: > > > The discussion about removing the side effect of irq_set_affinity_hint() of > > > actually applying the cpumask (if not NULL) as affinity to the interrupt, > > > unearthed a few unpleasantries: > > > > > > 1) The modular perf drivers rely on the current behaviour for the very > > > wrong reasons. > > > > > > 2) While none of the other drivers prevents user space from changing > > > the affinity, a cursorily inspection shows that there are at least > > > expectations in some drivers. > > > > > > #1 needs to be cleaned up anyway, so that's not a problem > > > > > > #2 might result in subtle regressions especially when irqbalanced (which > > > nowadays ignores the affinity hint) is disabled. > > > > > > Provide new interfaces: > > > > > > irq_update_affinity_hint() - Only sets the affinity hint pointer > > > irq_apply_affinity_hint() - Set the pointer and apply the affinity to > > > the interrupt > > > > > > Make irq_set_affinity_hint() a wrapper around irq_apply_affinity_hint() and > > > document it to be phased out. > > > > Is there recommended way to retrieve the CPU number that the interrupt has > > affinity? > > > > Previously a driver (I'm looking at drivers/net/ethernet/amazon/ena) that > > uses irq_set_affinity_hint() to spread out IRQ knows the corresponding CPU > > number since they're using their own spreading scheme. Now, phasing out > > irq_set_affinity_hint(), and thus relying on request_irq() to spread the > > load instead, there don't seem to be a easy way to get the CPU number. > > > > For drivers that don't want to rely on request_irq for spreading and want > to force their own affinity mask can use irq_set_affinity() I *do* want the driver to rely on request_irq() for spreading. It is retrieving effective affinity after request_irq() call that I can't seem to figure out. Thanks, Shung-Hsi > which is an exported interface now [1] and clearly indicates the purpose > of the usage. > > As Thomas suggested we are still keeping irq_set_affinity_hint() as a > wrapper until we make appropriate changes in individual drivers that use > this API for different reasons. Please feel free to send out a patch > for this driver once the changes are merged. > > [1] https://lkml.org/lkml/2021/5/18/271 > > -- > Thanks > Nitesh >
