RE: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

From: David Miller > Sent: 16 November 2015 20:32 > From: "Jason A. Donenfeld" > 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

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

From: "Jason A. Donenfeld" 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

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

From: "Jason A. Donenfeld" Date: Mon, 16 Nov 2015 22:28:52 +0100 > I'm making a simpler replacement for IPSec that operates as an > device driver on the interface level Someone already did a Linux implemenation of exactly that two decades ago, we rejected that design and did

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

On Mon, Nov 16, 2015 at 10:17 PM, David Miller wrote: > > Not without a complete redesign of the x86 fpu save/restore mechanism. Urg, okay. I still wonder why irq_fpu_usable() is true when using TCP but not when using UDP... Any ideas on this? > The driver is the wrong

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

Hi Jason, On Mon, Nov 16, 2015, at 21:58, Jason A. Donenfeld wrote: > Hi David, > > On Mon, Nov 16, 2015 at 9:32 PM, David Miller > wrote: > > Network device driver transmit executes with software interrupts > > disabled. > > > > Therefore on x86, you cannot use the FPU. >

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

On Mon, Nov 16, 2015 at 10:33 PM, David Miller wrote: > Someone already did a Linux implemenation of exactly that two decades > ago, we rejected that design and did what we did. It's not exactly IPSec though, so don't worry. It's a totally new thing that combines a lot of

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

From: "Jason A. Donenfeld" Date: Mon, 16 Nov 2015 21:58:49 +0100 > That is extremely problematic for me. Is there a way to make this > not so? Not without a complete redesign of the x86 fpu save/restore mechanism. The driver is the wrong place to do software cryptographic

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

Hi David, On Mon, Nov 16, 2015 at 9:32 PM, David Miller wrote: > Network device driver transmit executes with software interrupts > disabled. > > Therefore on x86, you cannot use the FPU. That is extremely problematic for me. Is there a way to make this not so? A driver

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

On Tue, Nov 17, 2015 at 12:57 AM, Jason A. Donenfeld wrote: > 2. irq_fpu_usable() is FALSE for UDP! Since in_interrupt() is always > true in ndo_start_xmit, this means that in this case, both > interrupted_user_mode() and interrupted_kernel_fpu_idle() are false! > Investigating

Re: irq_fpu_usable() is false in ndo_start_xmit() for UDP packets

Hi Hannes, Thanks for your response. On Mon, Nov 16, 2015 at 11:27 PM, Hannes Frederic Sowa wrote: > Use the irqsoff tracer to find the problematic functions which disable > interrupts and try to work around it in case of UDP. This could benefit > the whole stack. I