linux-kernel - Re: [PATCH 00/15] Coalesced Interrupt Delivery with posted MSI

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Date: Thu, 8 Feb 2024 08:34:55 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 LKML <linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, iommu@...ts.linux.dev,
 Thomas Gleixner <tglx@...utronix.de>, Lu Baolu <baolu.lu@...ux.intel.com>,
 kvm@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
 Joerg Roedel <joro@...tes.org>, "H. Peter Anvin" <hpa@...or.com>,
 Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>
Cc: Paul Luse <paul.e.luse@...el.com>, Dan Williams
 <dan.j.williams@...el.com>, Raj Ashok <ashok.raj@...el.com>,
 "Tian, Kevin" <kevin.tian@...el.com>, maz@...nel.org, seanjc@...gle.com,
 Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 00/15] Coalesced Interrupt Delivery with posted MSI

Hi Jacob,

I gave this a quick spin, using 4 gen2 optane drives. Basic test, just
IOPS bound on the drive, and using 1 thread per drive for IO. Random
reads, using io_uring.

For reference, using polled IO:

IOPS=20.36M, BW=9.94GiB/s, IOS/call=31/31
IOPS=20.36M, BW=9.94GiB/s, IOS/call=31/31
IOPS=20.37M, BW=9.95GiB/s, IOS/call=31/31

which is abount 5.1M/drive, which is what they can deliver.

Before your patches, I see:

IOPS=14.37M, BW=7.02GiB/s, IOS/call=32/32
IOPS=14.38M, BW=7.02GiB/s, IOS/call=32/31
IOPS=14.38M, BW=7.02GiB/s, IOS/call=32/31
IOPS=14.37M, BW=7.02GiB/s, IOS/call=32/32

at 2.82M ints/sec. With the patches, I see:

IOPS=14.73M, BW=7.19GiB/s, IOS/call=32/31
IOPS=14.90M, BW=7.27GiB/s, IOS/call=32/31
IOPS=14.90M, BW=7.27GiB/s, IOS/call=31/32

at 2.34M ints/sec. So a nice reduction in interrupt rate, though not
quite at the extent I expected. Booted with 'posted_msi' and I do see
posted interrupts increasing in the PMN in /proc/interrupts, 

Probably want to fold this one in:

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 8e09d40ea928..a289282f1cf9 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -393,7 +393,7 @@ void intel_posted_msi_init(void)
  * instead of:
  *		read, xchg, read, xchg, read, xchg, read, xchg
  */
-static __always_inline inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
+static __always_inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
 {
 	int i, vec = FIRST_EXTERNAL_VECTOR;
 	unsigned long pir_copy[4];

-- 
Jens Axboe