linux-kernel - Re: [PATCH] net/skbuff: silence warnings under memory pressure

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Date:   Fri, 6 Sep 2019 11:50:22 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Qian Cai <cai@....pw>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure

On (09/05/19 13:14), Steven Rostedt wrote:
> > Hmm, from the article,
> > 
> > https://en.wikipedia.org/wiki/Universal_asynchronous_receiver-transmitter
> > 
> > "Since transmission of a single or multiple characters may take a long time
> > relative to CPU speeds, a UART maintains a flag showing busy status so that the
> > host system knows if there is at least one character in the transmit buffer or
> > shift register; "ready for next character(s)" may also be signaled with an
> > interrupt."
> 
> I'm pretty sure all serial consoles do a busy loop on the UART and not
> use interrupts to notify when it's available.

Yes. Besides, we call console drivers with local IRQs disabled.

	-ss