[PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY)
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From: Darren Hart on 18 May 2010 17:40 From ad81664794e33d785f533c5edee37aaba20dd92d Mon Sep 17 00:00:00 2001 From: Darren Hart <dvhltc(a)us.ibm.com> Date: Tue, 18 May 2010 11:07:13 -0700 Subject: [PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY) The underlying hardware is edge triggered but presented by XICS as level triggered. The edge triggered interrupts are not reissued after masking. This is not a problem in mainline which does not mask the interrupt (relying on the EOI mechanism instead). The threaded interrupts in PREEMPT_RT do mask the interrupt, and can lose interrupts that occurred while masked, resulting in a hung ethernet interface. The receive handler simply calls napi_schedule(), as such, there is no significant additional overhead in making this non-threaded, since we either wakeup the threaded irq handler to call napi_schedule(), or just call napi_schedule() directly to wakeup the softirqs. As the receive handler is lockless, there is no need to convert any of the ehea spinlock_t's to atomic_spinlock_t's. Without this patch, a simple scp file copy loop would fail quickly (usually seconds). We have over two hours of sustained scp activity with the patch applied. Credit goes to Will Schmidt for lots of instrumentation and tracing which clarified the scenario and to Thomas Gleixner for the incredibly simple solution. Signed-off-by: Darren Hart <dvhltc(a)us.ibm.com> Acked-by: Will Schmidt <will_schmidt(a)vnet.ibm.com> Cc: Thomas Gleixner <tglx(a)linuxtronix.de> Cc: Jan-Bernd Themann <themann(a)de.ibm.com> Cc: Nivedita Singhvi <niv(a)us.ibm.com> Cc: Brian King <bjking1(a)us.ibm.com> Cc: Michael Ellerman <ellerman(a)au1.ibm.com> Cc: Doug Maxey <doug.maxey(a)us.ibm.com> --- drivers/net/ehea/ehea_main.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/drivers/net/ehea/ehea_main.c b/drivers/net/ehea/ehea_main.c index 977c3d3..2c53df2 100644 --- a/drivers/net/ehea/ehea_main.c +++ b/drivers/net/ehea/ehea_main.c @@ -1263,7 +1263,7 @@ static int ehea_reg_interrupts(struct net_device *dev) "%s-queue%d", dev->name, i); ret = ibmebus_request_irq(pr->eq->attr.ist1, ehea_recv_irq_handler, - IRQF_DISABLED, pr->int_send_name, + IRQF_DISABLED | IRQF_NODELAY, pr->int_send_name, pr); if (ret) { ehea_error("failed registering irq for ehea_queue " -- 1.5.5.6 -- Darren Hart IBM Linux Technology Center Real-Time Linux Team -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |