On 2019-01-15 12:44:53 [+0000], David Laight wrote: > Once this is done it might be worth while adding a parameter to > kernel_fpu_begin() to request the registers only when they don't > need saving. > This would benefit code paths where the gains are reasonable but not massive. So if saving + FPU code is a small win why not do this always? > The return value from kernel_fpu_begin() ought to indicate which > registers are available - none, SSE, SSE2, AVX, AVX512 etc. > So code can use an appropriate implementation. > (I've not looked to see if this is already the case!) Either everything is saved or nothing. So if SSE registers are saved then AVX512 are, too. I would like to see some benefit of this first before adding/adjusting the API in a way which makes it possible do something to do wrong. That said, one thing I would like to do is to get rid of irq_fpu_usable() so code can use FPU registers and needs not to implement a fallback. > David Sebastian
