linux-kernel - Re: [PATCH v5 8/8] selftests/resctrl: Adjust effective L3 cache size when SNC enabled

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Message-ID: <frfa3olxop3xjnouvvv7y2s36varmto5qwhmkitvslmiawzwkd@zh2jhob4o5qe>
Date:   Wed, 30 Aug 2023 15:08:33 +0200
From:   Maciej Wieczór-Retman 
        <maciej.wieczor-retman@...el.com>
To:     Tony Luck <tony.luck@...el.com>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Peter Newman <peternewman@...gle.com>,
        "Jonathan Corbet" <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, <x86@...nel.org>,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Babu Moger <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <patches@...ts.linux.dev>
Subject: Re: [PATCH v5 8/8] selftests/resctrl: Adjust effective L3 cache size
 when SNC enabled

Hello,

On 2023-08-29 at 16:44:26 -0700, Tony Luck wrote:
>Sub-NUMA Cluster divides CPUs sharing an L3 cache into separate NUMA
>nodes. Systems may support splitting into either two or four nodes.
>
>When SNC mode is enabled the effective amount of L3 cache available
>for allocation is divided by the number of nodes per L3.
>
>Detect which SNC mode is active by comparing the number of CPUs
>that share a cache with CPU0, with the number of CPUs on node0.
>
>This gives some hope of tests passing. But additional test
>infrastructure changes are needed to bind tests to nodes and
>guarantee memory allocation from the local node.
>
>Reported-by: "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>
>Signed-off-by: Tony Luck <tony.luck@...el.com>
>---
> tools/testing/selftests/resctrl/resctrl.h   |  1 +
> tools/testing/selftests/resctrl/resctrlfs.c | 57 +++++++++++++++++++++
> 2 files changed, 58 insertions(+)
>
>diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
>index 87e39456dee0..a8b43210b573 100644
>--- a/tools/testing/selftests/resctrl/resctrl.h
>+++ b/tools/testing/selftests/resctrl/resctrl.h
>@@ -13,6 +13,7 @@
> #include <signal.h>
> #include <dirent.h>
> #include <stdbool.h>
>+#include <ctype.h>
> #include <sys/stat.h>
> #include <sys/ioctl.h>
> #include <sys/mount.h>
>diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
>index fb00245dee92..79eecbf9f863 100644
>--- a/tools/testing/selftests/resctrl/resctrlfs.c
>+++ b/tools/testing/selftests/resctrl/resctrlfs.c
>@@ -130,6 +130,61 @@ int get_resource_id(int cpu_no, int *resource_id)
> 	return 0;
> }
> 
>+/*
>+ * Count number of CPUs in a /sys bit map
>+ */
>+static int count_sys_bitmap_bits(char *name)
>+{
>+	FILE *fp = fopen(name, "r");
>+	int count = 0, c;
>+
>+	if (!fp)
>+		return 0;
>+
>+	while ((c = fgetc(fp)) != EOF) {
>+		if (!isxdigit(c))
>+			continue;
>+		switch (c) {
>+		case 'f':
>+			count++;
>+		case '7': case 'b': case 'd': case 'e':
>+			count++;
>+		case '3': case '5': case '6': case '9': case 'a': case 'c':
>+			count++;
>+		case '1': case '2': case '4': case '8':
>+			count++;
>+		}
>+	}
>+	fclose(fp);
>+
>+	return count;
>+}
>+

The resctrl selftest has a function for counting bits, could it be used
here instead of the switch statement like this for example?

count = count_bits(c);

Or is there some reason this wouldn't be a good fit here?

-- 
Kind regards
Maciej Wieczór-Retman