From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH v2 2/3] kvm tools: remove periodic tick in favour of a polling thread Date: Wed, 04 Sep 2013 14:01:48 -0400 Message-ID: <5227758C.3000908@oracle.com> References: <1378301148-18823-1-git-send-email-jonathan.austin@arm.com> <1378301148-18823-3-git-send-email-jonathan.austin@arm.com> <52277097.8020008@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Jonathan Austin , KVM General , Marc Zyngier , Will Deacon , Matt Evans , Asias He To: Pekka Enberg Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:30385 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759429Ab3IDSCE (ORCPT ); Wed, 4 Sep 2013 14:02:04 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 09/04/2013 01:48 PM, Pekka Enberg wrote: > On Wed, Sep 4, 2013 at 8:40 PM, Jonathan Austin wrote: >> 'top' works on ARM with virtio console. I've just done some new testing >> and with the serial console emulation and I see the same as you're reporting. >> Previously with the 8250 emulation I'd booted to a prompt but didn't actually >> test top... >> >> I'm looking in to fixing this now... Looks like I need to find the right place >> from which to call serial8250_flush_tx now that it isn't getting called every tick. >> >> I've done the following and it works fixes 'top' with serial8250: >> -------8<---------- >> diff --git a/tools/kvm/hw/serial.c b/tools/kvm/hw/serial.c >> index 931067f..a71e68d 100644 >> --- a/tools/kvm/hw/serial.c >> +++ b/tools/kvm/hw/serial.c >> @@ -260,6 +260,7 @@ static bool serial8250_out(struct ioport *ioport, struct kvm *kvm, u16 port, >> dev->lsr &= ~UART_LSR_TEMT; >> if (dev->txcnt == FIFO_LEN / 2) >> dev->lsr &= ~UART_LSR_THRE; >> + serial8250_flush_tx(kvm, dev); >> } else { >> /* Should never happpen */ >> dev->lsr &= ~(UART_LSR_TEMT | UART_LSR_THRE); >> >> ------------->8----------- >> >> I guess it's a shame that we'll be printing each character (admittedly the rate will always be >> relatively low...) rather than flushing the buffer in a batch. Without a timer, though, I'm >> not sure I see a better option - every N chars doesn't seem like a good one to me. >> >> If you think that looks about right then I'll fold that in to the patch series, probably also >> removing the call to serial8250_flush_tx() in serial8250__receive. > > Yeah, looks good to me and makes top work again. We might want to make sure performance isn't hit with stuff that's intensive on the serial console. Thanks, Sasha