On 10/7/24 20:39, Joanne Koong wrote: > On Tue, Oct 1, 2024 at 10:03 AM Joanne Koong <joannelkoong@xxxxxxxxx> wrote: >> >> On Sat, Sep 28, 2024 at 1:43 AM Bernd Schubert >> <bernd.schubert@xxxxxxxxxxx> wrote: >>> >>> Hi Joanne, >>> >>> On 9/27/24 21:36, Joanne Koong wrote: >>>> On Mon, Sep 2, 2024 at 3:38 AM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >>>>> >>>>> On Fri, 30 Aug 2024 at 18:27, Joanne Koong <joannelkoong@xxxxxxxxx> wrote: >>>>>> >>>>>> There are situations where fuse servers can become unresponsive or >>>>>> stuck, for example if the server is in a deadlock. Currently, there's >>>>>> no good way to detect if a server is stuck and needs to be killed >>>>>> manually. >>>>>> >>>>>> This commit adds an option for enforcing a timeout (in seconds) on >>>>>> requests where if the timeout elapses without a reply from the server, >>>>>> the connection will be automatically aborted. >>>>> >>>>> Okay. >>>>> >>>>> I'm not sure what the overhead (scheduling and memory) of timers, but >>>>> starting one for each request seems excessive. >>>> >>>> I ran some benchmarks on this using the passthrough_ll server and saw >>>> roughly a 1.5% drop in throughput (from ~775 MiB/s to ~765 MiB/s): >>>> fio --name randwrite --ioengine=sync --thread --invalidate=1 >>>> --runtime=300 --ramp_time=10 --rw=randwrite --size=1G --numjobs=4 >>>> --bs=4k --alloc-size 98304 --allrandrepeat=1 --randseed=12345 >>>> --group_reporting=1 --directory=/root/fuse_mount >>>> >>>> Instead of attaching a timer to each request, I think we can instead >>>> do the following: >>>> * add a "start_time" field to each request tracking (in jiffies) when >>>> the request was started >>>> * add a new list to the connection that all requests get enqueued >>>> onto. When the request is completed, it gets dequeued from this list >>>> * have a timer for the connection that fires off every 10 seconds or >>>> so. When this timer is fired, it checks if "jiffies > req->start_time >>>> + fc->req_timeout" against the head of the list to check if the >>>> timeout has expired and we need to abort the request. We only need to >>>> check against the head of the list because we know every other request >>>> after this was started later in time. I think we could even just use >>>> the fc->lock for this instead of needing a separate lock. In the worst >>>> case, this grants a 10 second upper bound on the timeout a user >>>> requests (eg if the user requests 2 minutes, in the worst case the >>>> timeout would trigger at 2 minutes and 10 seconds). >>>> >>>> Also, now that we're aborting the connection entirely on a timeout >>>> instead of just aborting the request, maybe it makes sense to change >>>> the timeout granularity to minutes instead of seconds. I'm envisioning >>>> that this timeout mechanism will mostly be used as a safeguard against >>>> malicious or buggy servers with a high timeout configured (eg 10 >>>> minutes), and minutes seems like a nicer interface for users than them >>>> having to convert that to seconds. >>>> >>>> Let me know if I've missed anything with this approach but if not, >>>> then I'll submit v7 with this change. >>> >>> >>> sounds great to me. Just, could we do this per fuse_dev to avoid a >>> single lock for all cores? >>> >> >> Will do! thanks for the suggestion - in that case, I'll add its own >> spinlock for it too then. > > I realized while working on v7 that we can't do this per fuse device > because the request is only associated with a device once it's read in > by the server (eg fuse_dev_do_read). > > I ran some rough preliminary benchmarks with > ./libfuse/build/example/passthrough_ll -o writeback -o max_threads=4 > -o source=~/fstests ~/fuse_mount > and > fio --name randwrite --ioengine=sync --thread --invalidate=1 > --runtime=300 --ramp_time=10 --rw=randwrite --size=1G --numjobs=4 > --bs=4k --alloc-size 98304 --allrandrepeat=1 --randseed=12345 > --group_reporting=1 --directory=fuse_mount > > and didn't see any noticeable difference in throughput (~37 MiB/sec on > my system) with vs without the timeout. > That is not much, isn't your limit the backend? I wonder what would happen with 25GB/s I'm testing with. Wouldn't it make sense for this to test with sequential large IO? And possibly with the passthrough-hp branch that bypasses IO? And a NUMA system probably would be helpful as well. I.e. to test the effect on the kernel side without having an IO limited system? With the io-uring interface requests stay in queues from the in-coming CPU so easier to achieve there, although I wonder for your use-case if it wouldn't be sufficient to start the timer only when the request is on the way to fuse-server? One disadvantage I see is that virtiofs would need to be specially handled. Thanks, Bernd
