Peter Zijlstra <pet...@infradead.org> writes: > On Tue, Jun 10, 2014 at 02:29:17PM +0200, Rasmus Villemoes wrote: >> This is an attempt to reduce the stack footprint of various functions >> (those using any of the wait_event_* macros), by removing the need to >> allocate a wait_queue_t on the stack and instead use a single instance >> embedded in task_struct. I'm not really sure where the best place to >> put it is; I just placed it next to other list bookkeeping fields. >> >> For now, there is a little unconditional debugging. This could later >> be removed or maybe be made dependent on some CONFIG_* variable. The >> idea of using ->flags is taken from Pavel [1] (I originally stored >> (void*)1 into ->private). >> >> Compiles, but not actually tested. >> > > Doesn't look too bad, would be good to be tested and have some numbers > on the amount of stack saved etc..
Here are some numbers, and the fact that it only has a positive effect on 28 functions, together with Oleg's concerns, makes me think that it's probably not worth it. (defconfig on x86_64, based on 3.15) file function old new delta vmlinux i915_pipe_crc_read 120 136 +16 vmlinux try_to_free_pages 144 136 -8 vmlinux mousedev_read 112 96 -16 vmlinux sky2_probe 192 176 -16 vmlinux gss_cred_init 136 120 -16 vmlinux do_coredump 296 280 -16 vmlinux md_do_sync 360 344 -16 vmlinux save_image_lzo 200 168 -32 vmlinux read_events 184 152 -32 vmlinux loop_make_request 96 64 -32 vmlinux i801_access 104 72 -32 vmlinux tty_port_block_til_ready 104 72 -32 vmlinux loop_thread 152 120 -32 vmlinux evdev_read 136 104 -32 vmlinux __sb_start_write 96 64 -32 vmlinux rfkill_fop_read 104 72 -32 vmlinux intel_dp_aux_ch 152 120 -32 vmlinux i801_transaction 96 64 -32 vmlinux blk_mq_queue_enter 96 64 -32 vmlinux cypress_send_ext_cmd 152 104 -48 vmlinux rcu_gp_kthread 120 72 -48 vmlinux locks_mandatory_area 264 216 -48 vmlinux hub_thread 232 184 -48 vmlinux start_this_handle 120 72 -48 vmlinux autofs4_wait 136 88 -48 vmlinux fcntl_setlk 136 88 -48 vmlinux load_module 264 216 -48 vmlinux serport_ldisc_read 144 96 -48 vmlinux sg_read 160 112 -48 Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
