Messages in this thread | | | Subject | Re: [Bug] Take more 150s to boot qemu on ARM64 | From | "chenxiang (M)" <> | Date | Tue, 14 Jun 2022 09:53:30 +0800 |
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在 2022/6/13 21:22, Paul E. McKenney 写道: > On Mon, Jun 13, 2022 at 08:26:34PM +0800, chenxiang (M) wrote: >> Hi all, >> >> I encounter a issue with kernel 5.19-rc1 on a ARM64 board: it takes about >> 150s between beginning to run qemu command and beginng to boot Linux kernel >> ("EFI stub: Booting Linux Kernel..."). >> >> But in kernel 5.18-rc4, it only takes about 5s. I git bisect the kernel code >> and it finds c2445d387850 ("srcu: Add contention check to call_srcu() >> srcu_data ->lock acquisition"). >> >> The qemu (qemu version is 6.2.92) command i run is : >> >> ./qemu-system-aarch64 -m 4G,slots=4,maxmem=8g \ >> --trace "kvm*" \ >> -cpu host \ >> -machine virt,accel=kvm,gic-version=3 \ >> -machine smp.cpus=2,smp.sockets=2 \ >> -no-reboot \ >> -nographic \ >> -monitor unix:/home/cx/qmp-test,server,nowait \ >> -bios /home/cx/boot/QEMU_EFI.fd \ >> -kernel /home/cx/boot/Image \ >> -device pcie-root-port,port=0x8,chassis=1,id=net1,bus=pcie.0,multifunction=on,addr=0x1 >> \ >> -device vfio-pci,host=7d:01.3,id=net0 \ >> -device virtio-blk-pci,drive=drive0,id=virtblk0,num-queues=4 \ >> -drive file=/home/cx/boot/boot_ubuntu.img,if=none,id=drive0 \ >> -append "rdinit=init console=ttyAMA0 root=/dev/vda rootfstype=ext4 rw " \ >> -net none \ >> -D /home/cx/qemu_log.txt >> >> I am not familiar with rcu code, and don't know how it causes the issue. Do >> you have any idea about this issue? > Please see the discussion here: > > https://lore.kernel.org/all/20615615-0013-5adc-584f-2b1d5c03ebfc@linaro.org/ > > Though that report requires ACPI to be forced on to get the > delay, which results in more than 9,000 back-to-back calls to > synchronize_srcu_expedited(). I cannot reproduce this on my setup, even > with an artificial tight loop invoking synchronize_srcu_expedited(), > but then again I don't have ARM hardware. > > My current guess is that the following patch, but with larger values for > SRCU_MAX_NODELAY_PHASE. Here "larger" might well be up in the hundreds, > or perhaps even larger. > > If you get a chance to experiment with this, could you please reply > to the discussion at the above URL? (Or let me know, and I can CC > you on the next message in that thread.)
Ok, thanks, i will reply it on above URL.
> > Thanx, Paul > > ------------------------------------------------------------------------ > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 50ba70f019dea..0db7873f4e95b 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -513,7 +513,7 @@ static bool srcu_readers_active(struct srcu_struct *ssp) > > #define SRCU_INTERVAL 1 // Base delay if no expedited GPs pending. > #define SRCU_MAX_INTERVAL 10 // Maximum incremental delay from slow readers. > -#define SRCU_MAX_NODELAY_PHASE 1 // Maximum per-GP-phase consecutive no-delay instances. > +#define SRCU_MAX_NODELAY_PHASE 3 // Maximum per-GP-phase consecutive no-delay instances. > #define SRCU_MAX_NODELAY 100 // Maximum consecutive no-delay instances. > > /* > @@ -522,16 +522,22 @@ static bool srcu_readers_active(struct srcu_struct *ssp) > */ > static unsigned long srcu_get_delay(struct srcu_struct *ssp) > { > + unsigned long gpstart; > + unsigned long j; > unsigned long jbase = SRCU_INTERVAL; > > if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), READ_ONCE(ssp->srcu_gp_seq_needed_exp))) > jbase = 0; > - if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))) > - jbase += jiffies - READ_ONCE(ssp->srcu_gp_start); > - if (!jbase) { > - WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1); > - if (READ_ONCE(ssp->srcu_n_exp_nodelay) > SRCU_MAX_NODELAY_PHASE) > - jbase = 1; > + if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))) { > + j = jiffies - 1; > + gpstart = READ_ONCE(ssp->srcu_gp_start); > + if (time_after(j, gpstart)) > + jbase += j - gpstart; > + if (!jbase) { > + WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1); > + if (READ_ONCE(ssp->srcu_n_exp_nodelay) > SRCU_MAX_NODELAY_PHASE) > + jbase = 1; > + } > } > return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase; > } > . >
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