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Message-Id: <20210316050801.2446401-2-jim.cromie@gmail.com>
Date: Mon, 15 Mar 2021 23:07:44 -0600
From: Jim Cromie <jim.cromie@...il.com>
To: jbaron@...mai.com, gregkh@...uxfoundation.org,
linux-kernel@...r.kernel.org
Cc: Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH v3 01/18] dyndbg: split struct _ddebug, move display fields to new _ddebug_site
struct _ddebug has 2 flavors of fields: essential and optional. Split
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
select callsites to >control. lineno is arguably optional too, but
leaving it uses spare bytes in struct _ddebug.
The new ptr increases memory footprint by 1 ptr per pr_debug, but I
think its temporary, and the indirection gives several advantages:
- we can drop sites and their storage opportunistically.
this reduces per-site mem by 24/64.
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");
- 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.
IFF we can on-demand map: ddebugs[N] -> ddebug_sites[N]
- we can compress __dyndbg_sites during __init, and mark section __initdata
- can decompress on-demand, say for `cat control`
- can save chunks of decompressed buffer for enabled callsites
- free chunks on site disable, or on memory pressure.
Whats actually done here is rather mechanical, and preparatory.
dynamic_debug.h:
I cut struct _ddebug in half, renamed 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 head.site to
point at body.
DECLARE_DYNAMIC_DEBUG_METADATA does the core of the work; it declares
and initializes both static struct variables together, and refs one to
the other.
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 move 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 | 46 +++++++++++++++++--------------
3 files changed, 53 insertions(+), 33 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 a57ee75342cf..bc8027292c02 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 site 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
@@ -44,8 +52,7 @@ struct _ddebug {
struct static_key_false dd_key_false;
} key;
#endif
-} __attribute__((aligned(8)));
-
+} __aligned(8);
#if defined(CONFIG_DYNAMIC_DEBUG_CORE)
@@ -83,11 +90,15 @@ 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 c70d6347afa2..738c4ce28046 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -142,7 +142,7 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
/*
* Search the tables for _ddebug's which match the given `query' and
* apply the `flags' and `mask' to them. Returns number of matching
- * callsites, normally the same as number of changes. If verbose,
+ * sites, normally the same as number of changes. If verbose,
* logs the changes. Takes ddebug_lock.
*/
static int ddebug_change(const struct ddebug_query *query,
@@ -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));
}
}
@@ -586,14 +587,15 @@ 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;
*buf = '\0';
- 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
@@ -601,15 +603,15 @@ 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)
@@ -879,6 +881,7 @@ 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) {
@@ -887,9 +890,11 @@ 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");
@@ -1093,17 +1098,17 @@ 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++;
@@ -1113,9 +1118,10 @@ 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') {
--
2.29.2
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