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ethtool: Correct description of 'max_coalesced_frames' fields

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The current descriptions state that these fields specify 'How many
packets to delay ... after a packet ...' which implies that the
hardware should wait for (max_coalesced_frames + 1) completions before
generating an interrupt.  It is also stated that setting both this
field and the corresponding 'coalesce_usecs' field to 0 is invalid.
Together, this implies that the hardware must always be configured
to delay a completion IRQ for at least 1 usec or 1 more completion.

I believe that the addition of 1 is not intended, and David Miller
confirms that the original implementation (in tg3) does not do this.
Clarify the descriptions of these fields to avoid this interpretation.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ben Hutchings 2011-08-15 14:07:47 +00:00 committed by David S. Miller
parent 725b361b29
commit 2d7c79390e
1 changed files with 13 additions and 13 deletions
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26
include/linux/ethtool.h
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@ -122,8 +122,8 @@ struct ethtool_eeprom {
* @cmd: ETHTOOL_{G,S}COALESCE
* @rx_coalesce_usecs: How many usecs to delay an RX interrupt after
* a packet arrives. If 0, only @rx_max_coalesced_frames is used.
* @rx_max_coalesced_frames: How many packets to delay an RX interrupt
* after a packet arrives. If 0, only @rx_coalesce_usecs is used.
* @rx_max_coalesced_frames: Maximum number of packets to receive
* before an RX interrupt. If 0, only @rx_coalesce_usecs is used.
* @rx_coalesce_usecs_irq: Same as @rx_coalesce_usecs, except that
* this value applies while an IRQ is being serviced by the host.
* @rx_max_coalesced_frames_irq: Same as @rx_max_coalesced_frames,
@ -132,9 +132,9 @@ struct ethtool_eeprom {
* @tx_coalesce_usecs: How many usecs to delay a TX interrupt after
* a packet is sent. If 0, only @tx_max_coalesced_frames
* is used.
* @tx_max_coalesced_frames: How many packets to delay a TX interrupt
* after a packet is sent. If 0, only @tx_coalesce_usecs is
* used.
* @tx_max_coalesced_frames: Maximum number of packets to be sent
* before a TX interrupt. If 0, only @tx_coalesce_usecs is
* used.
* @tx_coalesce_usecs_irq: Same as @tx_coalesce_usecs, except that
* this value applies while an IRQ is being serviced by the host.
* @tx_max_coalesced_frames_irq: Same as @tx_max_coalesced_frames,
@ -149,21 +149,21 @@ struct ethtool_eeprom {
* @pkt_rate_low: Threshold for low packet rate (packets per second).
* @rx_coalesce_usecs_low: How many usecs to delay an RX interrupt after
* a packet arrives, when the packet rate is below @pkt_rate_low.
* @rx_max_coalesced_frames_low: How many packets to delay an RX interrupt
* after a packet arrives, when the packet rate is below @pkt_rate_low.
* @rx_max_coalesced_frames_low: Maximum number of packets to be received
* before an RX interrupt, when the packet rate is below @pkt_rate_low.
* @tx_coalesce_usecs_low: How many usecs to delay a TX interrupt after
* a packet is sent, when the packet rate is below @pkt_rate_low.
* @tx_max_coalesced_frames_low: How many packets to delay a TX interrupt
* after a packet is sent, when the packet rate is below @pkt_rate_low.
* @tx_max_coalesced_frames_low: Maximum nuumber of packets to be sent before
* a TX interrupt, when the packet rate is below @pkt_rate_low.
* @pkt_rate_high: Threshold for high packet rate (packets per second).
* @rx_coalesce_usecs_high: How many usecs to delay an RX interrupt after
* a packet arrives, when the packet rate is above @pkt_rate_high.
* @rx_max_coalesced_frames_high: How many packets to delay an RX interrupt
* after a packet arrives, when the packet rate is above @pkt_rate_high.
* @rx_max_coalesced_frames_high: Maximum number of packets to be received
* before an RX interrupt, when the packet rate is above @pkt_rate_high.
* @tx_coalesce_usecs_high: How many usecs to delay a TX interrupt after
* a packet is sent, when the packet rate is above @pkt_rate_high.
* @tx_max_coalesced_frames_high: How many packets to delay a TX interrupt
* after a packet is sent, when the packet rate is above @pkt_rate_high.
* @tx_max_coalesced_frames_high: Maximum number of packets to be sent before
* a TX interrupt, when the packet rate is above @pkt_rate_high.
* @rate_sample_interval: How often to do adaptive coalescing packet rate
* sampling, measured in seconds. Must not be zero.
*