[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 00/25 v7] SBSA UART emulation support in Xen
Hi Julien, Thanks for the testing. On 8 August 2017 at 21:29, Julien Grall <julien.grall@xxxxxxx> wrote: > Hi Bhupinder, > > I gave another and I have a couple of comments. > > Booting Linux with earlycon enabled take quite a while. I can see the > characters coming slower than on the minitel. It seems to be a bit better > after switching off the bootconsole. Overall Linux is taking ~20 times to > boot with pl011 vs HVC console. > > I do agree that pl011 is emulated and therefore you have to trap after each > character. But 20 times sounds far too much. > I think this slowness could be due to ratelimiting of the pl011 events in xenconosle. Currently, the rate limit is set to 30 events per 200 msecs (see RATE_LIMIT_ALLOWANCE/RATE_LIMIT_PERIOD). I increased the rate limit to 600 events (30 * 20) per 200 msecs. With this change, I see that the the find command is running faster and smoother. Earlier the find output would be jerky. > After that I tried to stress the emulation a bit with "find ." to get a lot > of output. And I noticed a lot of message similar to the one below on xen > console: > > d6v0 vpl011: Unexpected OUT ring buffer full > > Associated to that the character have been eaten resulting to non-sense log. > > A bit above the printk printing this message, there are a comment saying: > > /* > * It is expected that the ring is not full when this function is called > * as the guest is expected to write to the data register only when the > * TXFF flag is not set. > * In case the guest does write even when the TXFF flag is set then the > * data will be silently dropped. > */ > > I am quite surprised that Linux is not looking at the TXFF flags. So this > needs some investigation. I ran 'find' but could not reproduce the issue. I will try to reproduce this issue by reducing the OUT buffer size. Regards, Bhupinder _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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