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3c395a969a
For the Timer IRQ mode (i.e., when command completions are delayed), there is one timer for each CPU. Each of these timers . has a completion queue associated with it, containing all the command completions to be executed when the timer fires; . is set, and a new completion-to-execute is inserted into its completion queue, every time the dispatch code for a new command happens to be executed on the CPU related to the timer. This implies that, if the dispatch of a new command happens to be executed on a CPU whose timer has already been set, but has not yet fired, then the timer is set again, to the completion time of the newly arrived command. When the timer eventually fires, all its queued completions are executed. This way of handling delayed command completions entails the following problem: if more than one command completion is inserted into the queue of a timer before the timer fires, then the expiration time for the timer is moved forward every time each of these completions is enqueued. As a consequence, only the last completion enqueued enjoys a correct execution time, while all previous completions are unjustly delayed until the last completion is executed (and at that time they are executed all together). Specifically, if all the above completions are enqueued almost at the same time, then the problem is negligible. On the opposite end, if every completion is enqueued a while after the previous completion was enqueued (in the extreme case, it is enqueued only right before the timer would have expired), then every enqueued completion, except for the last one, experiences an inflated delay, proportional to the number of completions enqueued after it. In the end, commands, and thus I/O requests, may be completed at an arbitrarily lower rate than the desired one. This commit addresses this issue by replacing per-CPU timers with per-command timers, i.e., by associating an individual timer with each command. Signed-off-by: Paolo Valente <paolo.valente@unimore.it> Signed-off-by: Arianna Avanzini <avanzini@google.com> Signed-off-by: Jens Axboe <axboe@fb.com> |
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| aoe | ||
| drbd | ||
| mtip32xx | ||
| paride | ||
| rsxx | ||
| xen-blkback | ||
| zram | ||
| amiflop.c | ||
| ataflop.c | ||
| brd.c | ||
| cciss.c | ||
| cciss.h | ||
| cciss_cmd.h | ||
| cciss_scsi.c | ||
| cciss_scsi.h | ||
| cpqarray.c | ||
| cpqarray.h | ||
| cryptoloop.c | ||
| DAC960.c | ||
| DAC960.h | ||
| floppy.c | ||
| hd.c | ||
| ida_cmd.h | ||
| ida_ioctl.h | ||
| Kconfig | ||
| loop.c | ||
| loop.h | ||
| Makefile | ||
| mg_disk.c | ||
| nbd.c | ||
| null_blk.c | ||
| osdblk.c | ||
| pktcdvd.c | ||
| ps3disk.c | ||
| ps3vram.c | ||
| rbd.c | ||
| rbd_types.h | ||
| skd_main.c | ||
| skd_s1120.h | ||
| smart1,2.h | ||
| sunvdc.c | ||
| swim.c | ||
| swim3.c | ||
| swim_asm.S | ||
| sx8.c | ||
| umem.c | ||
| umem.h | ||
| virtio_blk.c | ||
| xen-blkfront.c | ||
| xsysace.c | ||
| z2ram.c | ||