Messages in this thread Patch in this message | | | Date | Wed, 5 Sep 2018 13:53:59 +1000 | From | Nicholas Piggin <> | Subject | Re: VirtIO console hangs |
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On Fri, 31 Aug 2018 15:17:44 +0000 Matteo Croce <mcroce@redhat.com> wrote:
> On Fri, Aug 31, 2018 at 3:49 AM Nicholas Piggin <npiggin@gmail.com> wrote: > > > > On Tue, 28 Aug 2018 15:00:14 +0000 > > Matteo Croce <mcroce@redhat.com> wrote: > > > > > On Tue, Aug 28, 2018 at 2:35 PM Nicholas Piggin <npiggin@gmail.com> wrote: > > > > > > > > On Tue, 28 Aug 2018 12:54:08 +0000 > > > > Matteo Croce <mcroce@redhat.com> wrote: > > > > > > > > > With kernel 4.19.0-rc1 virtio_console hangs very often. > > > > > I can always trigger the bug by pasting some characters in the > > > > > terminal window, the console will stop receiving keypresses, but I can > > > > > still see output from the console. > > > > > Stangely, logging in the VM via SSH and sending lot of data to hvc0, > > > > > like 'dmesg >/dev/hvc0' will fix the issue until the next paste. > > > > > > > > > > I did a git bisect and I've found that this is the offending commit, > > > > > reverting it fixes it. > > > > > > > > > > Cheers, > > > > > > > > > > commit ec97eaad1383ab2500fcf9a07ade6044fbcc67f5 > > > > > Author: Nicholas Piggin <npiggin@gmail.com> > > > > > Date: Tue May 1 00:55:54 2018 +1000 > > > > > > > > > > tty: hvc: hvc_poll() break hv read loop > > > > > > > > Thanks for the report. I can't immediately see what the problem > > > > is. Can you try get a stack trace of where it is stuck? > > > > > > > > > > I tried but didn't get one. > > > > > > > Perhaps try this patch if you have time (it's a bit of a shot > > > > in the dark). > > > > > > > > > > Yes it seems to fix. Thanks! > > > > Okay sorry for the delay, I can reproduce it here and found a better > > fix, if I could trouble you to test again. > > > > [PATCH] tty: hvc: hvc_poll() fix read loop hang > > > > Hi Nicholas, > > the patch works, but now pasting text inside the terminal is extremely > slow, it feels worse than a 9600 baud serial line. > > Btw, I had to apply the patch by hand as it was corrupted, some lines > were collapsed into one.
Not sure why that happened, I seem to be able to send myself uncorrupted patches...
Can you try this patch for performance? Hopefully it applies. --
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 5414c4a87bea..f5fc3ba49130 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -49,6 +49,8 @@ #define N_OUTBUF 16 #define N_INBUF 16 +#define HVC_ATOMIC_READ_MAX 128 + #define __ALIGNED__ __attribute__((__aligned__(sizeof(long)))) static struct tty_driver *hvc_driver; @@ -522,6 +524,8 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count return -EIO; while (count > 0) { + int ret; + spin_lock_irqsave(&hp->lock, flags); rsize = hp->outbuf_size - hp->n_outbuf; @@ -537,10 +541,13 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count } if (hp->n_outbuf > 0) - hvc_push(hp); + ret = hvc_push(hp); spin_unlock_irqrestore(&hp->lock, flags); + if (!ret) + break; + if (count) { if (hp->n_outbuf > 0) hvc_flush(hp); @@ -669,8 +676,8 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep) if (!hp->irq_requested) poll_mask |= HVC_POLL_READ; + read_again: /* Read data if any */ - count = tty_buffer_request_room(&hp->port, N_INBUF); /* If flip is full, just reschedule a later read */ @@ -717,9 +724,23 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep) #endif /* CONFIG_MAGIC_SYSRQ */ tty_insert_flip_char(&hp->port, buf[i], 0); } - if (n == count) - poll_mask |= HVC_POLL_READ; - read_total = n; + read_total += n; + + if (may_sleep) { + /* Keep going until the flip is full */ + spin_unlock_irqrestore(&hp->lock, flags); + cond_resched(); + spin_lock_irqsave(&hp->lock, flags); + goto read_again; + } else if (read_total < HVC_ATOMIC_READ_MAX) { + /* Break and defer if it's a large read in atomic */ + goto read_again; + } + + /* + * Latency break, schedule another poll immediately. + */ + poll_mask |= HVC_POLL_READ; out: /* Wakeup write queue if necessary */
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