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From: David Miller <davem@davemloft.net>
To: Jason@zx2c4.com
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets
Date: Mon, 16 Nov 2015 15:32:14 -0500 (EST)	[thread overview]
Message-ID: <20151116.153214.1125103075112383723.davem@davemloft.net> (raw)
In-Reply-To: <CAHmME9qQz-uTFDjUuVaqpO9ODt3KZWEdYVQJ8qsXWa5YkYAoWA@mail.gmail.com>

From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Mon, 16 Nov 2015 20:52:28 +0100

> This works fine with, say, iperf3 in TCP mode. The AVX performance
> is great. However, when using iperf3 in UDP mode, irq_fpu_usable()
> is mostly false! I added a dump_stack() call to see why, except
> nothing looks strange; the initial call in the stack trace is
> entry_SYSCALL_64_fastpath. Why would irq_fpu_usable() return false
> when we're in a syscall? Doesn't that mean this is in process
> context?

Network device driver transmit executes with software interrupts
disabled.

Therefore on x86, you cannot use the FPU.

  reply	other threads:[~2015-11-16 20:32 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-16 19:52 irq_fpu_usable() is false in ndo_start_xmit() for UDP packets Jason A. Donenfeld
2015-11-16 20:32 ` David Miller [this message]
2015-11-16 20:58   ` Jason A. Donenfeld
2015-11-16 21:17     ` David Miller
2015-11-16 21:28       ` Jason A. Donenfeld
2015-11-16 21:33         ` David Miller
2015-11-16 21:37           ` Jason A. Donenfeld
2015-11-16 22:27     ` Hannes Frederic Sowa
2015-11-16 23:57       ` Jason A. Donenfeld
2015-11-17  0:04         ` Jason A. Donenfeld
2015-11-17 12:38   ` David Laight

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