On 09/10/2012 07:58 PM, Tony Lindgren wrote: > * Jon Hunter <jon-hunter@xxxxxx> [120910 15:00]: >> >> On 09/07/2012 05:22 PM, Tony Lindgren wrote: >>> * Jon Hunter <jon-hunter@xxxxxx> [120905 12:05]: >>>> The dmtimer functions to read and write the dmtimer registers are currently >>>> defined as follows ... >>>> >>>> static inline u32 __omap_dm_timer_read(struct omap_dm_timer *timer, u32 reg, >>>> int posted); >>>> static inline void __omap_dm_timer_write(struct omap_dm_timer *timer, >>>> u32 reg, u32 val, int posted); >>>> >>>> The posted variable indicates if the timer is configured to use the posted mode >>>> when performing register accesses. The posted mode configuration of the dmtimer >>>> is stored in the omap_dm_timer structure that is also being passed to the above >>>> functions and therefore we do not need to pass the posted variable separately. >>>> Therefore, simplify the above functions by removing the posted variable as an >>>> argument as this is not necessary. >>> >>> I believe the reason for passing the posted flag was to optimize out some >>> functions from the timer code as that's being run all the time. >>> >>> Care to check the assembly before and after this patch for the timer >>> functions with objdump -d to make sure it does not add tons of bloat >>> there? >> >> Hi Tony, >> >> Thanks for the details here. I see that makes sense and that the >> compiler could take advantage of this as the functions are inlined. >> >> I have taken a look at the disassembled output using objdump as you >> mentioned. What I see is ... >> >> 1. For dmtimer.c the impact appears negligible, the total number of >> lines outputted by objdump only changed by 8 with (1215 lines) and >> without (1207 lines) the patch applied. >> >> 2. For timer.c the impact is greater. I see that >> omap2_gp_timer_set_next_event() increased by 6 instructions from 29 >> to 35. clocksource_read_cycles() increased by 2 instructions 15 to >> 17 instructions. dmtimer_read_sched_clock() increased by 2 >> instructions from 17 to 19. omap2_gp_timer_set_mode() increased by >> 21 instructions from 102 to 123. >> >> I imagine that we are mainly concerned about >> omap2_gp_timer_set_next_event(), clocksource_read_cycles() and >> dmtimer_read_sched_clock() as these will be called often. Therefore, I >> am not sure if you wish to drop this patch. > > Well does it at lots of new ldr to the critical code? For the omap2_gp_timer_set_next_event() function it adds 3 load instructions, increasing the number of possible loads from 11 to 14. For the clocksource_read_cycles() function it adds 1 load instruction, increasing the number of possible loads from 7 to 8. For the dmtimer_read_sched_clock() function, I don't see any additional loads, but instructions added are a tst and beq instruction. >> By the way, if we do drop this patch, I would then need to fix the >> setting of the posted variable in mach-omap2/timer.c for clock-source in >> the case where a dmtimer is used. Today the code assumes that for >> clock-source and clock-events posted mode is always used. However, with >> the errata i103/i767 we will disable posted mode for clock-source on >> omap2/3/4/5/am33xx devices. > > Yes I see, I guess that means just adding a new systimer entry? Actually, I think we can avoid that by not using posted mode for clock-source timers at all. Posted mode only benefits the clock-events timers that are configured often. The benefit of not using posted mode for clock-source timers and setting the "posted" parameter to 0, will really allow the compiler to optimise the clocksource_read_cycles() and dmtimer_read_sched_clock() quite a bit. So this could be a nice optimisation. Cheers Jon -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
