> -----Original Message----- > From: Finn Thain [mailto:fthain@xxxxxxxxxxxxxxxxxxx] > Sent: Tuesday, February 9, 2021 6:06 PM > To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx> > Cc: tanxiaofei <tanxiaofei@xxxxxxxxxx>; jejb@xxxxxxxxxxxxx; > martin.petersen@xxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; linuxarm@xxxxxxxxxxxxx; > linux-m68k@xxxxxxxxxxxxxxx > Subject: RE: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization > for SCSI drivers > > On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote: > > > > -----Original Message----- > > > From: Finn Thain [mailto:fthain@xxxxxxxxxxxxxxxxxxx] > > > Sent: Monday, February 8, 2021 8:57 PM > > > To: tanxiaofei <tanxiaofei@xxxxxxxxxx> > > > Cc: jejb@xxxxxxxxxxxxx; martin.petersen@xxxxxxxxxx; > > > linux-scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > > linuxarm@xxxxxxxxxxxxx > > > Subject: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization > > > for SCSI drivers > > > > > > 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. If you put your Sorry for I didn't realize xiaofei had replied. > 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. > > 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. > 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
