Warner Losh 3f2e5b8584 After the introduction of direct dispatch, the pacing code in g_down() ... broke in two ways. One, the pacing variable was accessed in multiple threads in an unsafe way. Two, since large numbers of I/O could come down from the buf layer at one time, large numbers of allocation failures could happen all at once, resulting in a huge pace value that would limit I/Os to 10 IOPS for minutes (or even hours) at a time. While a real solution to these problems requires substantial work (to go to a no-allocation after the first model, or to have some way to wait for more memory with some kind of reserve for pager and swapper requests), it is relatively easy to make this simplistic pacing less pathological. Move to using a volatile variable with loads and stores. While this is a little racy, losing the race is safe: either you get memory and proceed, or you don't and queue. Second, sleep for 1ms (or one tick, whichever is larger) instead of 100ms. This removes the artificial 10 IOPS limit while still easing up on new I/Os during memory shortages. Remove tying the amount of time we do this to the number of failed requests and do it only as long as we keep failing requests. Finally, to avoid needless recursion when memory is tight (start -> g_io_deliver() -> g_io_request() -> start -> ... until we use 1/2 the stack), don't do direct dispatch while pacing. This should be a rare event (not steady state) so the performance hit here is worth the extra safety of not starving g_down() with directly dispatched I/O. Differential Review: https://reviews.freebsd.org/D3546		2015-09-02 17:29:30 +00:00
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bde
cache
concat
eli	Enable BIO_DELETE passthru in GELI, so TRIM/UNMAP can work as expected when	2015-08-08 09:51:38 +00:00
gate
journal
label
linux_lvm
mirror
mountver
multipath
nop
part	Report the scheme and provider names in warning message about unaligned	2015-07-26 11:16:48 +00:00
raid	Clean out some externally visible "more then" grammar	2015-08-11 03:12:09 +00:00
raid3
sched
shsec
stripe
uncompress	Make some debug printf's into DPRINTF's to reduce noise on attach/detahh	2015-08-09 06:58:06 +00:00
uzip	Make some debug printf's into DPRINTF's to reduce noise on attach/detach	2015-08-06 15:30:14 +00:00
vinum
virstor
zero
geom_aes.c
geom_bsd_enc.c
geom_bsd.c
geom_ccd.c
geom_ctl.c
geom_ctl.h
geom_dev.c	Fix panic triggered by code like this:	2015-08-04 10:40:08 +00:00
geom_disk.c
geom_disk.h
geom_dump.c
geom_event.c
geom_flashmap.c	Create a RouterBoard platform and use it to create a flash map	2015-08-22 05:50:18 +00:00
geom_fox.c
geom_int.h
geom_io.c	After the introduction of direct dispatch, the pacing code in g_down()	2015-09-02 17:29:30 +00:00
geom_kern.c
geom_map.c
geom_mbr_enc.c
geom_mbr.c
geom_pc98_enc.c
geom_pc98.c
geom_redboot.c
geom_slice.c
geom_slice.h
geom_subr.c
geom_sunlabel_enc.c
geom_sunlabel.c
geom_vfs.c
geom_vfs.h
geom_vol_ffs.c
geom.h
notes