Messages in this thread | | | Subject | Re: [PATCH] serial: core: prevent softlockups on slow consoles | From | Peter Hurley <> | Date | Fri, 4 Sep 2015 06:42:26 -0400 |
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On 09/04/2015 03:19 AM, Vitaly Kuznetsov wrote: > Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
>> I don't like this, please narrow this down to the real problem that your >> hardware has here, the putchar function should not be this slow. If it >> is, something is wrong. > > I'm afraid this is really the case: > > 3) | serial8250_console_putchar() { > 3) | wait_for_xmitr() { > 3) # 3111.189 us | io_serial_in(); > 3) # 3115.334 us | } > 3) # 2234.099 us | io_serial_out(); > 3) # 5353.883 us | } > > This is one char and I use local pipe for Hyper-V output. In case > something like remote pipe is in use ... > > So I'm sorry, but I don't really understand the suggestion to 'narrow > this down' - this is how slow Hyper-V serial's implementation is, > io_serial_in() is just an inb() and io_serial_out() is an outb().
That corresponds to 330-440 baud. As far as I'm concerned, that's broken.
Regards, Peter Hurley
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