On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote: > > On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote: > > > > > > On Sun, 7 Feb 2021, Xiaofei Tan wrote: > > > > > > > > > Replace spin_lock_irqsave with spin_lock in hard IRQ of SCSI > > > > > drivers. There are no function changes, but may speed up if > > > > > interrupt happen too often. > > > > > > > > This change doesn't necessarily work on platforms that support > > > > nested interrupts. > > > > > > > > Were you able to measure any benefit from this change on some > > > > other platform? > > > > > > I think the code disabling irq in hardIRQ is simply wrong. Since > > > this commit > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e58aa3d2d0cc > > > genirq: Run irq handlers with interrupts disabled > > > > > > interrupt handlers are definitely running in a irq-disabled context > > > unless irq handlers enable them explicitly in the handler to permit > > > other interrupts. > > > > > > > Repeating the same claim does not somehow make it true. > > Sorry for I didn't realize xiaofei had replied. > I was referring to the claim in patch 00/32, i.e. that interrupt handlers only run when irqs are disabled. > > If you put your claim to the test, you'll see that that interrupts are > > not disabled on m68k when interrupt handlers execute. > > Sounds like an implementation issue of m68k since IRQF_DISABLED has been > totally removed. > It's true that IRQF_DISABLED could be used to avoid the need for irq locks in interrupt handlers. So, if you want to remove irq locks from interrupt handlers, today you can't use IRQF_DISABLED to help you. So what? > > > > The Interrupt Priority Level (IPL) can prevent any given irq handler > > from being re-entered, but an irq with a higher priority level may be > > handled during execution of a lower priority irq handler. > > > > We used to have IRQF_DISABLED to support so-called "fast interrupt" to > avoid this. > > But the concept has been totally removed. That is interesting if m68k > still has this issue. > Prioritized interrupts are beneficial. Why would you want to avoid them? Moreover, there's no reason to believe that m68k is the only platform that supports nested interrupts. > > sonic_interrupt() uses an irq lock within an interrupt handler to > > avoid issues relating to this. This kind of locking may be needed in > > the drivers you are trying to patch. Or it might not. Apparently, > > no-one has looked. > > Thanks > Barry >
