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a0458b07c1
sh port of the sLeAZY-fpu feature currently implemented for some architectures such us i386. Right now the SH kernel has a 100% lazy fpu behaviour. This is of course great for applications that have very sporadic or no FPU use. However for very frequent FPU users... you take an extra trap every context switch. The patch below adds a simple heuristic to this code: after 5 consecutive context switches of FPU use, the lazy behavior is disabled and the context gets restored every context switch. After 256 switches, this is reset and the 100% lazy behavior is returned. Tests with LMbench showed no regression. I saw a little improvement due to the prefetching (~2%). The tests below also show that, with this sLeazy patch, indeed, the number of FPU exceptions is reduced. To test this. I hacked the lat_ctx LMBench to use the FPU a little more. sLeasy implementation =========================================== switch_to calls | 79326 sleasy calls | 42577 do_fpu_state_restore calls| 59232 restore_fpu calls | 59032 Exceptions: 0x800 (FPU disabled ): 16604 100% Leazy (default implementation) =========================================== switch_to calls | 79690 do_fpu_state_restore calls | 53299 restore_fpu calls | 53101 Exceptions: 0x800 (FPU disabled ): 53273 Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com> Signed-off-by: Stuart Menefy <stuart.menefy@st.com> Signed-off-by: Paul Mundt <lethal@linux-sh.org> |
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| kernel | ||
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| math-emu | ||
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| Kconfig | ||
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