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Subjecte1000 horridness (was Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected)


On Tue, 26 Aug 2008, Jeff Garzik wrote:
>
> e1000_check_options builds a struct (singular) on the stack, really... struct
> e1000_option is reasonably small.

No it doesn't.

Look a bit more closely.

It builds a struct (singular) MANY MANY times. It also then builds up a
huge e1000_opt_list[] array, even though it is const and should be static
(and const).

I know. I wrote a patch to FIX it.

Here's the patch. It shrinks the stack from 1152 bytes to 192 bytes (the
first version, that only did the e1000_option part, got it down to 600
bytes). About half comes from not using multiple "e1000_option"
structures, the other half comes from turning the "e1000_opt_list[]"
arrays into "static const" instead, so that gcc doesn't copy them onto the
stack.
Most of the patch is actually doing things like turning

struct struct e1000_option opt = {
(which declares a _new_ e1000_option variable each time) into

opt = (struct e1000_option) {
which just re-uses the single variable.

It becomes slightly larger than that, because some places the "opt = .."
had to be moved around, since it's no longer a variable declaration, but a
regular assignment.
The rest is just adding "const" to the right places, and turning

struct e1000_opt_list speed_list[] = ..

into

static const struct e1000_opt_list speed_list[] = ..

instead, and fixing the indentation to be more straightforward.

I have not tested the dang thing, but I think it's correct. And it turns
stack usage from "totally horrible and broken" into "pretty reasonable".

Linus

---
drivers/net/e1000/e1000_param.c | 81 +++++++++++++++++++++-----------------
1 files changed, 45 insertions(+), 36 deletions(-)
diff --git a/drivers/net/e1000/e1000_param.c b/drivers/net/e1000/e1000_param.c
index b9f90a5..213437d 100644
--- a/drivers/net/e1000/e1000_param.c
+++ b/drivers/net/e1000/e1000_param.c
@@ -208,7 +208,7 @@ struct e1000_option {
} r;
struct { /* list_option info */
int nr;
- struct e1000_opt_list { int i; char *str; } *p;
+ const struct e1000_opt_list { int i; char *str; } *p;
} l;
} arg;
};
@@ -242,7 +242,7 @@ static int __devinit e1000_validate_option(unsigned int *value,
break;
case list_option: {
int i;
- struct e1000_opt_list *ent;
+ const struct e1000_opt_list *ent;

for (i = 0; i < opt->arg.l.nr; i++) {
ent = &opt->arg.l.p[i];
@@ -279,7 +279,9 @@ static void e1000_check_copper_options(struct e1000_adapter *adapter);

void __devinit e1000_check_options(struct e1000_adapter *adapter)
{
+ struct e1000_option opt;
int bd = adapter->bd_number;
+
if (bd >= E1000_MAX_NIC) {
DPRINTK(PROBE, NOTICE,
"Warning: no configuration for board #%i\n", bd);
@@ -287,19 +289,21 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}

{ /* Transmit Descriptor Count */
- struct e1000_option opt = {
+ struct e1000_tx_ring *tx_ring = adapter->tx_ring;
+ int i;
+ e1000_mac_type mac_type = adapter->hw.mac_type;
+
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Transmit Descriptors",
.err = "using default of "
__MODULE_STRING(E1000_DEFAULT_TXD),
.def = E1000_DEFAULT_TXD,
- .arg = { .r = { .min = E1000_MIN_TXD }}
+ .arg = { .r = {
+ .min = E1000_MIN_TXD,
+ .max = mac_type < e1000_82544 ? E1000_MAX_TXD : E1000_MAX_82544_TXD
+ }}
};
- struct e1000_tx_ring *tx_ring = adapter->tx_ring;
- int i;
- e1000_mac_type mac_type = adapter->hw.mac_type;
- opt.arg.r.max = mac_type < e1000_82544 ?
- E1000_MAX_TXD : E1000_MAX_82544_TXD;

if (num_TxDescriptors > bd) {
tx_ring->count = TxDescriptors[bd];
@@ -313,19 +317,21 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
tx_ring[i].count = tx_ring->count;
}
{ /* Receive Descriptor Count */
- struct e1000_option opt = {
+ struct e1000_rx_ring *rx_ring = adapter->rx_ring;
+ int i;
+ e1000_mac_type mac_type = adapter->hw.mac_type;
+
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Receive Descriptors",
.err = "using default of "
__MODULE_STRING(E1000_DEFAULT_RXD),
.def = E1000_DEFAULT_RXD,
- .arg = { .r = { .min = E1000_MIN_RXD }}
+ .arg = { .r = {
+ .min = E1000_MIN_RXD,
+ .max = mac_type < e1000_82544 ? E1000_MAX_RXD : E1000_MAX_82544_RXD
+ }}
};
- struct e1000_rx_ring *rx_ring = adapter->rx_ring;
- int i;
- e1000_mac_type mac_type = adapter->hw.mac_type;
- opt.arg.r.max = mac_type < e1000_82544 ? E1000_MAX_RXD :
- E1000_MAX_82544_RXD;

if (num_RxDescriptors > bd) {
rx_ring->count = RxDescriptors[bd];
@@ -339,7 +345,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
rx_ring[i].count = rx_ring->count;
}
{ /* Checksum Offload Enable/Disable */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = enable_option,
.name = "Checksum Offload",
.err = "defaulting to Enabled",
@@ -363,7 +369,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
{ E1000_FC_FULL, "Flow Control Enabled" },
{ E1000_FC_DEFAULT, "Flow Control Hardware Default" }};

- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = list_option,
.name = "Flow Control",
.err = "reading default settings from EEPROM",
@@ -381,7 +387,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Transmit Interrupt Delay */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Transmit Interrupt Delay",
.err = "using default of " __MODULE_STRING(DEFAULT_TIDV),
@@ -399,7 +405,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Transmit Absolute Interrupt Delay */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Transmit Absolute Interrupt Delay",
.err = "using default of " __MODULE_STRING(DEFAULT_TADV),
@@ -417,7 +423,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Receive Interrupt Delay */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Receive Interrupt Delay",
.err = "using default of " __MODULE_STRING(DEFAULT_RDTR),
@@ -435,7 +441,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Receive Absolute Interrupt Delay */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Receive Absolute Interrupt Delay",
.err = "using default of " __MODULE_STRING(DEFAULT_RADV),
@@ -453,7 +459,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Interrupt Throttling Rate */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = range_option,
.name = "Interrupt Throttling Rate (ints/sec)",
.err = "using default of " __MODULE_STRING(DEFAULT_ITR),
@@ -497,7 +503,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Smart Power Down */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = enable_option,
.name = "PHY Smart Power Down",
.err = "defaulting to Disabled",
@@ -513,7 +519,7 @@ void __devinit e1000_check_options(struct e1000_adapter *adapter)
}
}
{ /* Kumeran Lock Loss Workaround */
- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = enable_option,
.name = "Kumeran Lock Loss Workaround",
.err = "defaulting to Enabled",
@@ -578,16 +584,18 @@ static void __devinit e1000_check_fiber_options(struct e1000_adapter *adapter)

static void __devinit e1000_check_copper_options(struct e1000_adapter *adapter)
{
+ struct e1000_option opt;
unsigned int speed, dplx, an;
int bd = adapter->bd_number;

{ /* Speed */
- struct e1000_opt_list speed_list[] = {{ 0, "" },
- { SPEED_10, "" },
- { SPEED_100, "" },
- { SPEED_1000, "" }};
+ static const struct e1000_opt_list speed_list[] = {
+ { 0, "" },
+ { SPEED_10, "" },
+ { SPEED_100, "" },
+ { SPEED_1000, "" }};

- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = list_option,
.name = "Speed",
.err = "parameter ignored",
@@ -604,11 +612,12 @@ static void __devinit e1000_check_copper_options(struct e1000_adapter *adapter)
}
}
{ /* Duplex */
- struct e1000_opt_list dplx_list[] = {{ 0, "" },
- { HALF_DUPLEX, "" },
- { FULL_DUPLEX, "" }};
+ static const struct e1000_opt_list dplx_list[] = {
+ { 0, "" },
+ { HALF_DUPLEX, "" },
+ { FULL_DUPLEX, "" }};

- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = list_option,
.name = "Duplex",
.err = "parameter ignored",
@@ -637,7 +646,7 @@ static void __devinit e1000_check_copper_options(struct e1000_adapter *adapter)
"parameter ignored\n");
adapter->hw.autoneg_advertised = AUTONEG_ADV_DEFAULT;
} else { /* Autoneg */
- struct e1000_opt_list an_list[] =
+ static const struct e1000_opt_list an_list[] =
#define AA "AutoNeg advertising "
{{ 0x01, AA "10/HD" },
{ 0x02, AA "10/FD" },
@@ -671,7 +680,7 @@ static void __devinit e1000_check_copper_options(struct e1000_adapter *adapter)
{ 0x2e, AA "1000/FD, 100/FD, 100/HD, 10/FD" },
{ 0x2f, AA "1000/FD, 100/FD, 100/HD, 10/FD, 10/HD" }};

- struct e1000_option opt = {
+ opt = (struct e1000_option) {
.type = list_option,
.name = "AutoNeg",
.err = "parameter ignored",

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