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Date: Tue, 11 May 2021 12:50:32 -0600
From: Jim Cromie <jim.cromie@...il.com>
To: Arnd Bergmann <arnd@...db.de>, Jason Baron <jbaron@...mai.com>,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH v5 03/28] dyndbg: split struct _ddebug's display fields to new _ddebug_site
Struct _ddebug has 2 kinds of fields: essential & optional/compressible.
Move the 3 optional fields: module, function, file into a new struct
_ddebug_site, and add pointer to it from _ddebug.
These fields are optional in that they are primarily used to generate
the optional "module:func:line" log prefix. They're also used to
display control, and to select callsites to >control. lineno is
arguably optional too, but it uses spare bytes in struct _ddebug, so
leaving it is free.
The "__dyndbg" ELF section contains the array of struct _ddebugs for
all the pr-debugs in the kernel/module. Reuse this pattern for the
new "__dyndbg_sites" section.
The new ptr increases memory footprint, but it is temporary
scaffolding; once we can map from _ddebugs[N] --> _ddebug_sites[N]
indirectly, we can drop site pointer, regaining worst case memory
parity with master.
The indirection gives several advantages:
- site ptr lets us decouple the 2 arrays
we can properly isolate dependencies by allowing null site
- the moved display fields are inherently hierarchical, and the linker
section is ordered; so (module, file, function) have repeating
values (90%, 85%, 45%). This is readily compressible, even with a
simple field-wise run length encoding. Since I'm splitting the struct,
I also reordered the fields to match the hierarchy.
- the separate linker section sets up naturally for block compression.
section compression at build time is practical - how ?
include/linux/decompress/generic.h has no corresponding compression
- we could drop sites and their storage opportunistically.
this could reduce per-site mem by 24/56.
Subsystems may not need/want "module:func:line:" in their logs.
If they already use format-prefixes such as "drm:kms:",
they can select on those, and don't need the site info for that.
forex:
#> echo module drm format "^drm:kms: " +p >control
ie: dynamic_debug_exec_queries("format '^drm:kms: '", "drm");
Once we can map: ddebugs[N] -> ddebug_sites[N], we can:
- compress __dyndbg_sites during __init, and mark section __initdata
- store the compressed block instead.
- decompress on-demand, stream for `cat control`
- save chunks of decompressed buffer for enabled callsites
- free chunks on site disable, or on memory pressure.
Whats actually done here is ths rather mechanical, and preparatory.
dynamic_debug.h:
I cut struct _ddebug in half, renamed the optional top-half to
_ddebug_site, kept __align(8) for both halves. I added a forward decl
for a unified comment for both head & body, and added _ddebug.site to
point at body.
DEFINE_DYNAMIC_DEBUG_METADATA now declares and initializes a 2nd
static struct var holding the _ddebug_site, and refs _ddebug to it.
dynamic_debug.c:
dynamic_debug_init() mem-usage now also counts sites.
dynamic_emit_prefix() & ddebug_change() use those moved fields; they
get a new initialized auto-var, and the field refs get adjusted as
needed to follow the field moves from one struct to the other.
struct _ddebug_site *dc = dp->site;
ddebug_proc_show() differs slightly; it assigns to (not initializes)
the autovar, to avoid a panic when p == SEQ_START_TOKEN.
vmlinux.lds.h:
add __dyndbg_sites section, with the same align(8) and KEEP as
used in the __dyndbg section.
Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
include/asm-generic/vmlinux.lds.h | 3 +++
include/linux/dynamic_debug.h | 37 +++++++++++++++++---------
lib/dynamic_debug.c | 44 ++++++++++++++++++-------------
3 files changed, 52 insertions(+), 32 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 0331d5d49551..4f2af9de2f03 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -353,6 +353,9 @@
*(__tracepoints) \
/* implement dynamic printk debug */ \
. = ALIGN(8); \
+ __start___dyndbg_sites = .; \
+ KEEP(*(__dyndbg_sites)) \
+ __stop___dyndbg_sites = .; \
__start___dyndbg = .; \
KEEP(*(__dyndbg)) \
__stop___dyndbg = .; \
diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index dce631e678dd..d56c02ed0c45 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -7,20 +7,28 @@
#endif
/*
- * An instance of this structure is created in a special
- * ELF section at every dynamic debug callsite. At runtime,
- * the special section is treated as an array of these.
+ * A pair of these structs are created in 2 special ELF sections
+ * (__dyndbg, __dyndbg_sites) for every dynamic debug callsite.
+ * At runtime, the sections are treated as arrays.
*/
-struct _ddebug {
+struct _ddebug;
+struct _ddebug_site {
/*
- * These fields are used to drive the user interface
- * for selecting and displaying debug callsites.
+ * These fields (and lineno) are used to:
+ * - decorate log messages per _ddebug.flags
+ * - select callsites for modification via >control
+ * - display callsites & settings in `cat control`
*/
const char *modname;
- const char *function;
const char *filename;
+ const char *function;
+} __aligned(8);
+
+struct _ddebug {
+ struct _ddebug_site *site;
+ /* format is always needed, lineno shares word with flags */
const char *format;
- unsigned int lineno:18;
+ const unsigned lineno:18;
/*
* The flags field controls the behaviour at the callsite.
* The bits here are changed dynamically when the user
@@ -49,8 +57,7 @@ struct _ddebug {
struct static_key_false dd_key_false;
} key;
#endif
-} __attribute__((aligned(8)));
-
+} __aligned(8);
#if defined(CONFIG_DYNAMIC_DEBUG_CORE)
@@ -88,11 +95,15 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
const char *fmt, ...);
#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
- static struct _ddebug __aligned(8) \
- __section("__dyndbg") name = { \
+ static struct _ddebug_site __aligned(8) \
+ __section("__dyndbg_sites") name##_site = { \
.modname = KBUILD_MODNAME, \
- .function = __func__, \
.filename = __FILE__, \
+ .function = __func__, \
+ }; \
+ static struct _ddebug __aligned(8) \
+ __section("__dyndbg") name = { \
+ .site = &name##_site, \
.format = (fmt), \
.lineno = __LINE__, \
.flags = _DPRINTK_FLAGS_DEFAULT, \
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 3a7d1f9bcf4d..c1c2c90ed944 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -165,19 +165,20 @@ static int ddebug_change(const struct ddebug_query *query,
for (i = 0; i < dt->num_ddebugs; i++) {
struct _ddebug *dp = &dt->ddebugs[i];
+ struct _ddebug_site *dc = dp->site;
/* match against the source filename */
if (query->filename &&
- !match_wildcard(query->filename, dp->filename) &&
+ !match_wildcard(query->filename, dc->filename) &&
!match_wildcard(query->filename,
- kbasename(dp->filename)) &&
+ kbasename(dc->filename)) &&
!match_wildcard(query->filename,
- trim_prefix(dp->filename)))
+ trim_prefix(dc->filename)))
continue;
/* match against the function */
if (query->function &&
- !match_wildcard(query->function, dp->function))
+ !match_wildcard(query->function, dc->function))
continue;
/* match against the format */
@@ -214,8 +215,8 @@ static int ddebug_change(const struct ddebug_query *query,
#endif
dp->flags = newflags;
v2pr_info("changed %s:%d [%s]%s =%s\n",
- trim_prefix(dp->filename), dp->lineno,
- dt->mod_name, dp->function,
+ trim_prefix(dc->filename), dp->lineno,
+ dt->mod_name, dc->function,
ddebug_describe_flags(dp->flags, &fbuf));
}
}
@@ -586,12 +587,13 @@ static int remaining(int wrote)
return 0;
}
-static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
+static char *__dynamic_emit_prefix(const struct _ddebug *dp, char *buf)
{
int pos_after_tid;
int pos = 0;
+ const struct _ddebug_site *desc = dp->site;
- if (desc->flags & _DPRINTK_FLAGS_INCL_TID) {
+ if (dp->flags & _DPRINTK_FLAGS_INCL_TID) {
if (in_interrupt())
pos += snprintf(buf + pos, remaining(pos), "<intr> ");
else
@@ -599,15 +601,15 @@ static char *__dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
task_pid_vnr(current));
}
pos_after_tid = pos;
- if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME)
+ if (dp->flags & _DPRINTK_FLAGS_INCL_MODNAME)
pos += snprintf(buf + pos, remaining(pos), "%s:",
desc->modname);
- if (desc->flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
+ if (dp->flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
pos += snprintf(buf + pos, remaining(pos), "%s:",
desc->function);
- if (desc->flags & _DPRINTK_FLAGS_INCL_LINENO)
+ if (dp->flags & _DPRINTK_FLAGS_INCL_LINENO)
pos += snprintf(buf + pos, remaining(pos), "%d:",
- desc->lineno);
+ dp->lineno);
if (pos - pos_after_tid)
pos += snprintf(buf + pos, remaining(pos), " ");
if (pos >= PREFIX_SIZE)
@@ -884,6 +886,7 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
{
struct ddebug_iter *iter = m->private;
struct _ddebug *dp = p;
+ struct _ddebug_site *dc;
struct flagsbuf flags;
if (p == SEQ_START_TOKEN) {
@@ -892,9 +895,11 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
return 0;
}
+ dc = dp->site;
+
seq_printf(m, "%s:%u [%s]%s =%s \"",
- trim_prefix(dp->filename), dp->lineno,
- iter->table->mod_name, dp->function,
+ trim_prefix(dc->filename), dp->lineno,
+ iter->table->mod_name, dc->function,
ddebug_describe_flags(dp->flags, &flags));
seq_escape(m, dp->format, "\t\r\n\"");
seq_puts(m, "\"\n");
@@ -1097,17 +1102,17 @@ static int __init dynamic_debug_init(void)
return 0;
}
iter = __start___dyndbg;
- modname = iter->modname;
+ modname = iter->site->modname;
iter_start = iter;
for (; iter < __stop___dyndbg; iter++) {
entries++;
- if (strcmp(modname, iter->modname)) {
+ if (strcmp(modname, iter->site->modname)) {
modct++;
ret = ddebug_add_module(iter_start, n, modname);
if (ret)
goto out_err;
n = 0;
- modname = iter->modname;
+ modname = iter->site->modname;
iter_start = iter;
}
n++;
@@ -1117,9 +1122,10 @@ static int __init dynamic_debug_init(void)
goto out_err;
ddebug_init_success = 1;
- vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in __dyndbg section\n",
+ vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in __dyndbg section, %d bytes in __dyndbg_sites section\n",
modct, entries, (int)(modct * sizeof(struct ddebug_table)),
- (int)(entries * sizeof(struct _ddebug)));
+ (int)(entries * sizeof(struct _ddebug)),
+ (int)(entries * sizeof(struct _ddebug_site)));
/* apply ddebug_query boot param, dont unload tables on err */
if (ddebug_setup_string[0] != '\0') {
--
2.31.1
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