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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v6 01/15] xen/common: add cache coloring common code
Last Level Cache (LLC) coloring allows to partition the cache in smaller
chunks called cache colors. Since not all architectures can actually
implement it, add a HAS_LLC_COLORING Kconfig and put other options under
xen/arch.
LLC colors are a property of the domain, so the domain struct has to be
extended.
Based on original work from: Luca Miccio <lucmiccio@xxxxxxxxx>
Signed-off-by: Carlo Nonato <carlo.nonato@xxxxxxxxxxxxxxx>
Signed-off-by: Marco Solieri <marco.solieri@xxxxxxxxxxxxxxx>
---
v6:
- moved almost all code in common
- moved documentation in this patch
- reintroduced range for CONFIG_NR_LLC_COLORS
- reintroduced some stub functions to reduce the number of checks on
llc_coloring_enabled
- moved domain_llc_coloring_free() in same patch where allocation happens
- turned "d->llc_colors" to pointer-to-const
- llc_coloring_init() now returns void and panics if errors are found
v5:
- used - instead of _ for filenames
- removed domain_create_llc_colored()
- removed stub functions
- coloring domain fields are now #ifdef protected
v4:
- Kconfig options moved to xen/arch
- removed range for CONFIG_NR_LLC_COLORS
- added "llc_coloring_enabled" global to later implement the boot-time
switch
- added domain_create_llc_colored() to be able to pass colors
- added is_domain_llc_colored() macro
---
docs/misc/cache-coloring.rst | 87 +++++++++++++++++++++++++++++++
docs/misc/xen-command-line.pandoc | 27 ++++++++++
xen/arch/Kconfig | 17 ++++++
xen/common/Kconfig | 3 ++
xen/common/Makefile | 1 +
xen/common/keyhandler.c | 3 ++
xen/common/llc-coloring.c | 87 +++++++++++++++++++++++++++++++
xen/include/xen/llc-coloring.h | 38 ++++++++++++++
xen/include/xen/sched.h | 5 ++
9 files changed, 268 insertions(+)
create mode 100644 docs/misc/cache-coloring.rst
create mode 100644 xen/common/llc-coloring.c
create mode 100644 xen/include/xen/llc-coloring.h
diff --git a/docs/misc/cache-coloring.rst b/docs/misc/cache-coloring.rst
new file mode 100644
index 0000000000..9fe01e99e1
--- /dev/null
+++ b/docs/misc/cache-coloring.rst
@@ -0,0 +1,87 @@
+Xen cache coloring user guide
+=============================
+
+The cache coloring support in Xen allows to reserve Last Level Cache (LLC)
+partitions for Dom0, DomUs and Xen itself. Currently only ARM64 is supported.
+
+To compile LLC coloring support set ``CONFIG_LLC_COLORING=y``.
+
+If needed, change the maximum number of colors with
+``CONFIG_NR_LLC_COLORS=<n>``.
+
+Compile Xen and the toolstack and then configure it via
+`Command line parameters`_.
+
+Background
+**********
+
+Cache hierarchy of a modern multi-core CPU typically has first levels dedicated
+to each core (hence using multiple cache units), while the last level is shared
+among all of them. Such configuration implies that memory operations on one
+core (e.g. running a DomU) are able to generate interference on another core
+(e.g .hosting another DomU). Cache coloring allows eliminating this
+mutual interference, and thus guaranteeing higher and more predictable
+performances for memory accesses.
+The key concept underlying cache coloring is a fragmentation of the memory
+space into a set of sub-spaces called colors that are mapped to disjoint cache
+partitions. Technically, the whole memory space is first divided into a number
+of subsequent regions. Then each region is in turn divided into a number of
+subsequent sub-colors. The generic i-th color is then obtained by all the
+i-th sub-colors in each region.
+
+::
+
+ Region j Region j+1
+ ..................... ............
+ . . .
+ . .
+ _ _ _______________ _ _____________________ _ _
+ | | | | | | |
+ | c_0 | c_1 | | c_n | c_0 | c_1 |
+ _ _ _|_____|_____|_ _ _|_____|_____|_____|_ _ _
+ : :
+ : :... ... .
+ : color 0
+ :........................... ... .
+ :
+ . . ..................................:
+
+There are two pragmatic lesson to be learnt.
+
+1. If one wants to avoid cache interference between two domains, different
+ colors needs to be used for their memory.
+
+2. Color assignment must privilege contiguity in the partitioning. E.g.,
+ assigning colors (0,1) to domain I and (2,3) to domain J is better than
+ assigning colors (0,2) to I and (1,3) to J.
+
+How to compute the number of colors
+***********************************
+
+To compute the number of available colors for a specific platform, the size of
+an LLC way and the page size used by Xen must be known. The first parameter can
+be found in the processor manual or can be also computed dividing the total
+cache size by the number of its ways. The second parameter is the minimum
+amount of memory that can be mapped by the hypervisor, thus dividing the way
+size by the page size, the number of total cache partitions is found. So for
+example, an Arm Cortex-A53 with a 16-ways associative 1 MiB LLC, can isolate up
+to 16 colors when pages are 4 KiB in size.
+
+Cache layout is probed automatically by looking at the CLIDR_EL1 arm register.
+This means that other system caches that aren't visible there, are ignored.
+The possibility of manually setting the way size is left to the user to
overcome
+failing situations or for debugging/testing purposes. See
+`Command line parameters`_ for more information on that.
+
+Command line parameters
+***********************
+
+More specific documentation is available at
`docs/misc/xen-command-line.pandoc`.
+
++----------------------+-------------------------------+
+| **Parameter** | **Description** |
++----------------------+-------------------------------+
+| ``llc-coloring`` | enable coloring at runtime |
++----------------------+-------------------------------+
+| ``llc-way-size`` | set the LLC way size |
++----------------------+-------------------------------+
diff --git a/docs/misc/xen-command-line.pandoc
b/docs/misc/xen-command-line.pandoc
index 8e65f8bd18..11f9f209d1 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1713,6 +1713,33 @@ This option is intended for debugging purposes only.
Enable MSR_DEBUGCTL.LBR
in hypervisor context to be able to dump the Last Interrupt/Exception To/From
record with other registers.
+### llc-coloring
+> `= <boolean>`
+
+> Default: `false`
+
+Flag to enable or disable LLC coloring support at runtime. This options is
+available only when `CONFIG_LLC_COLORING` is enabled. See the general
+cache coloring documentation for more info.
+
+### llc-way-size
+> `= <size>`
+
+> Default: `Obtained from the hardware`
+
+Specify the way size of the Last Level Cache. This options is available only
+when `CONFIG_LLC_COLORING` is enabled. It is an optional, expert-only parameter
+and it is used to calculate the number of available LLC colors on the platform.
+It can be obtained by dividing the total LLC size by the number of its
+associative ways.
+By default, the value is automatically computed by probing the hardware, but in
+case of specific needs, it can be manually set. Those include failing probing
+and debugging/testing purposes so that it's possibile to emulate platforms with
+different number of supported colors.
+An important detail to highlight is that the current implementation of the
+cache coloring technique requires the number of colors to be a power of 2, and
+consequently, also the LLC way size must be so.
+
### lock-depth-size
> `= <integer>`
diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
index 67ba38f32f..c1157bcbcb 100644
--- a/xen/arch/Kconfig
+++ b/xen/arch/Kconfig
@@ -31,3 +31,20 @@ config NR_NUMA_NODES
associated with multiple-nodes management. It is the upper bound of
the number of NUMA nodes that the scheduler, memory allocation and
other NUMA-aware components can handle.
+
+config LLC_COLORING
+ bool "Last Level Cache (LLC) coloring" if EXPERT
+ depends on HAS_LLC_COLORING
+
+config NR_LLC_COLORS
+ int "Maximum number of LLC colors"
+ range 2 1024
+ default 128
+ depends on LLC_COLORING
+ help
+ Controls the build-time size of various arrays associated with LLC
+ coloring. Refer to cache coloring documentation for how to compute the
+ number of colors supported by the platform. This is only an upper
+ bound. The runtime value is autocomputed or manually set via cmdline.
+ The default value corresponds to an 8 MiB 16-ways LLC, which should be
+ more than what needed in the general case.
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 310ad4229c..e383f09d97 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -71,6 +71,9 @@ config HAS_IOPORTS
config HAS_KEXEC
bool
+config HAS_LLC_COLORING
+ bool
+
config HAS_PMAP
bool
diff --git a/xen/common/Makefile b/xen/common/Makefile
index 69d6aa626c..409cc53e2a 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -24,6 +24,7 @@ obj-y += keyhandler.o
obj-$(CONFIG_KEXEC) += kexec.o
obj-$(CONFIG_KEXEC) += kimage.o
obj-$(CONFIG_LIVEPATCH) += livepatch.o livepatch_elf.o
+obj-$(CONFIG_LLC_COLORING) += llc-coloring.o
obj-$(CONFIG_MEM_ACCESS) += mem_access.o
obj-y += memory.o
obj-y += multicall.o
diff --git a/xen/common/keyhandler.c b/xen/common/keyhandler.c
index 99a2d72a02..8d90b613f7 100644
--- a/xen/common/keyhandler.c
+++ b/xen/common/keyhandler.c
@@ -6,6 +6,7 @@
#include <xen/debugger.h>
#include <xen/delay.h>
#include <xen/keyhandler.h>
+#include <xen/llc-coloring.h>
#include <xen/param.h>
#include <xen/shutdown.h>
#include <xen/event.h>
@@ -307,6 +308,8 @@ static void cf_check dump_domains(unsigned char key)
arch_dump_domain_info(d);
+ domain_dump_llc_colors(d);
+
rangeset_domain_printk(d);
dump_pageframe_info(d);
diff --git a/xen/common/llc-coloring.c b/xen/common/llc-coloring.c
new file mode 100644
index 0000000000..10729e70c1
--- /dev/null
+++ b/xen/common/llc-coloring.c
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Last Level Cache (LLC) coloring common code
+ *
+ * Copyright (C) 2022 Xilinx Inc.
+ */
+#include <xen/keyhandler.h>
+#include <xen/llc-coloring.h>
+#include <xen/param.h>
+
+bool __ro_after_init llc_coloring_enabled;
+boolean_param("llc-coloring", llc_coloring_enabled);
+
+/* Size of an LLC way */
+static unsigned int __ro_after_init llc_way_size;
+size_param("llc-way-size", llc_way_size);
+/* Number of colors available in the LLC */
+static unsigned int __ro_after_init max_nr_colors = CONFIG_NR_LLC_COLORS;
+
+static void print_colors(const unsigned int *colors, unsigned int num_colors)
+{
+ unsigned int i;
+
+ printk("{ ");
+ for ( i = 0; i < num_colors; i++ ) {
+ unsigned int start = colors[i], end = colors[i];
+
+ printk("%u", start);
+
+ for ( ;
+ i < num_colors - 1 && colors[i] + 1 == colors[i + 1];
+ i++, end++ );
+
+ if ( start != end )
+ printk("-%u", end);
+
+ if ( i < num_colors - 1 )
+ printk(", ");
+ }
+ printk(" }\n");
+}
+
+static void dump_coloring_info(unsigned char key)
+{
+ printk("'%c' pressed -> dumping LLC coloring general info\n", key);
+ printk("LLC way size: %u KiB\n", llc_way_size >> 10);
+ printk("Number of LLC colors supported: %u\n", max_nr_colors);
+}
+
+void __init llc_coloring_init(void)
+{
+ if ( !llc_way_size && !(llc_way_size = get_llc_way_size()) )
+ panic("Probed LLC coloring way size is 0 and no custom value found\n");
+
+ /*
+ * The maximum number of colors must be a power of 2 in order to correctly
+ * map them to bits of an address, so also the LLC way size must be so.
+ */
+ if ( llc_way_size & (llc_way_size - 1) )
+ panic("LLC coloring way size (%u) isn't a power of 2\n", llc_way_size);
+
+ max_nr_colors = llc_way_size >> PAGE_SHIFT;
+
+ if ( max_nr_colors < 2 || max_nr_colors > CONFIG_NR_LLC_COLORS )
+ panic("Number of LLC colors (%u) not in range [2, %u]\n",
+ max_nr_colors, CONFIG_NR_LLC_COLORS);
+
+ register_keyhandler('K', dump_coloring_info, "dump LLC coloring info", 1);
+
+ arch_llc_coloring_init();
+}
+
+void domain_dump_llc_colors(const struct domain *d)
+{
+ printk("Domain %pd has %u LLC colors: ", d, d->num_llc_colors);
+ print_colors(d->llc_colors, d->num_llc_colors);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/xen/llc-coloring.h b/xen/include/xen/llc-coloring.h
new file mode 100644
index 0000000000..5e12eb426f
--- /dev/null
+++ b/xen/include/xen/llc-coloring.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Last Level Cache (LLC) coloring common header
+ *
+ * Copyright (C) 2022 Xilinx Inc.
+ */
+#ifndef __COLORING_H__
+#define __COLORING_H__
+
+#include <xen/sched.h>
+#include <public/domctl.h>
+
+#ifdef CONFIG_LLC_COLORING
+extern bool llc_coloring_enabled;
+
+void llc_coloring_init(void);
+void domain_dump_llc_colors(const struct domain *d);
+#else
+#define llc_coloring_enabled false
+
+static inline void llc_coloring_init(void) {}
+static inline void domain_dump_llc_colors(const struct domain *d) {}
+#endif
+
+unsigned int get_llc_way_size(void);
+void arch_llc_coloring_init(void);
+
+#endif /* __COLORING_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 9da91e0e62..8df0f29335 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -626,6 +626,11 @@ struct domain
/* Holding CDF_* constant. Internal flags for domain creation. */
unsigned int cdf;
+
+#ifdef CONFIG_LLC_COLORING
+ unsigned const int *llc_colors;
+ unsigned int num_llc_colors;
+#endif
};
static inline struct page_list_head *page_to_list(
--
2.34.1
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