Messages in this thread |  | | | Date | Wed, 9 May 2007 15:18:31 -0700 | | From | Andrew Morton <> | | Subject | Re: aio is unlikely |
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On Wed, 09 May 2007 18:06:58 -0400 Jeff Garzik <jeff@garzik.org> wrote:
> > -#define in_aio() !is_sync_wait(current->io_wait) > > +#define in_aio() (unlikely(!is_sync_wait(current->io_wait))) > > Please revert. Workload-dependent "likelihood" should not cause > programmers to add such markers. > > This is a common misunderstanding about unlikely() and likely(). The > branch prediction used for each assumes 99% unlikely or 99% likely, > which is not true at all for workload-dependent code. > > Even if only 1% of Linux users use AIO, for that 1%, the 'unlikely' > marker causes repeated branch mispredictions. > > likely() and unlikely() should be used for cases where code is > likely/unlikely for EVERYBODY.
a) disagree with the above
b) if in_aio() ever returns true we do
printk(KERN_ERR "%s(%s:%d) called in async context!\n", __FUNCTION__, __FILE__, __LINE__);
so I sure hope it's unlikely for all workloads.
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