https://github.com/torvalds/linux
Revision f7bbb9098315d712351aba7861a8c9fcf6bf0213 authored by Auke Kok on 28 November 2007, 00:26:36 UTC, committed by Jeff Garzik on 01 December 2007, 21:32:32 UTC
Don't exit polling when we have not yet used our budget, this causes the NAPI system to end up with a messed up poll list. Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com> Signed-off-by: Jeff Garzik <jeff@garzik.org>
1 parent e970d1f
Tip revision: f7bbb9098315d712351aba7861a8c9fcf6bf0213 authored by Auke Kok on 28 November 2007, 00:26:36 UTC
e1000: Fix NAPI state bug when Rx complete
e1000: Fix NAPI state bug when Rx complete
Tip revision: f7bbb90
io_ordering.txt
On some platforms, so-called memory-mapped I/O is weakly ordered. On such
platforms, driver writers are responsible for ensuring that I/O writes to
memory-mapped addresses on their device arrive in the order intended. This is
typically done by reading a 'safe' device or bridge register, causing the I/O
chipset to flush pending writes to the device before any reads are posted. A
driver would usually use this technique immediately prior to the exit of a
critical section of code protected by spinlocks. This would ensure that
subsequent writes to I/O space arrived only after all prior writes (much like a
memory barrier op, mb(), only with respect to I/O).
A more concrete example from a hypothetical device driver:
...
CPU A: spin_lock_irqsave(&dev_lock, flags)
CPU A: val = readl(my_status);
CPU A: ...
CPU A: writel(newval, ring_ptr);
CPU A: spin_unlock_irqrestore(&dev_lock, flags)
...
CPU B: spin_lock_irqsave(&dev_lock, flags)
CPU B: val = readl(my_status);
CPU B: ...
CPU B: writel(newval2, ring_ptr);
CPU B: spin_unlock_irqrestore(&dev_lock, flags)
...
In the case above, the device may receive newval2 before it receives newval,
which could cause problems. Fixing it is easy enough though:
...
CPU A: spin_lock_irqsave(&dev_lock, flags)
CPU A: val = readl(my_status);
CPU A: ...
CPU A: writel(newval, ring_ptr);
CPU A: (void)readl(safe_register); /* maybe a config register? */
CPU A: spin_unlock_irqrestore(&dev_lock, flags)
...
CPU B: spin_lock_irqsave(&dev_lock, flags)
CPU B: val = readl(my_status);
CPU B: ...
CPU B: writel(newval2, ring_ptr);
CPU B: (void)readl(safe_register); /* maybe a config register? */
CPU B: spin_unlock_irqrestore(&dev_lock, flags)
Here, the reads from safe_register will cause the I/O chipset to flush any
pending writes before actually posting the read to the chipset, preventing
possible data corruption.
Computing file changes ...