From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: [PATCH v3] serial: 8250: convert to threaded IRQ Date: Thu, 7 Dec 2017 14:45:09 +0000 Message-ID: <20171207144509.482b3e45@alans-desktop> References: <20171204152627.23906-1-dzagorui@cisco.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20171204152627.23906-1-dzagorui@cisco.com> Sender: linux-kernel-owner@vger.kernel.org To: Denys Zagorui Cc: gregkh@linuxfoundation.org, jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-serial@vger.kernel.org On Mon, 4 Dec 2017 17:26:27 +0200 Denys Zagorui wrote: > During using virtualization it is common to see > many "too much work for irq*" messages. Your emulator is buggy. NAK You are adding a ton of overhead to an absolutely performance critical path on real hardware. We absolutely cannot have 16450 or 16550A UARTS being serviced via a threaded IRQ. Fix your emulator. You are getting the problem because your serial port emulation isn't doing timing correct queueing of characters. If you are modelling 115,200 baud then don't queue characters faster than that or batch them excessively. We went to 512 as the pass limit to allow virtualization layers to get this right more easily as you don't have to do timing on tiny batches. (And if you need performance of any kind stop using the uart emulation and use virtio) Alan