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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Marc =?utf-8?Q?Str=C3=A4mke?= <marc.straemke@eltropuls.de>
Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Subject: Re: Latency spikes on V6.15.1 Preempt RT and maybe related to intel?
 IGB
Message-ID: <20250617092814.vqKdu23w@linutronix.de>
References: <20250613145434.T2x2ML8_@linutronix.de>
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 <20250613195838.0-gZ6bqS@linutronix.de>
 <97638b0b-cd96-40e2-9dc2-5e6f767b90a4@eltropuls.de>
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In-Reply-To: <97638b0b-cd96-40e2-9dc2-5e6f767b90a4@eltropuls.de>

On 2025-06-14 10:52:36 [+0200], Marc Str=C3=A4mke wrote:
>               ip-4931    [001] b...3   700.149995: igb_update_mc_addr_lis=
t <-igb_set_rx_mode
>               ip-4931    [001] Dn..3   700.150795: irq_disable: caller=3D=
irqentry_enter+0x2a/0x60 parent=3D0x0

Between those two functions you have 800us delay. Interrupts are not
disabled so the CPU stalls. As explained earlier, I expect the read on
the bus flushes the writes causing the spike.

Sebastian