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    Subject[PATCH 2/2] I/OAT: tcp_dma_copybreak default value dependant on I/OAT version
    Date
    I/OAT DMA performance tuning showed different optimal values 
    of tcp_dma_copybreak for different I/OAT versions
    (4096 for 1.2 and 2048 for 2.0).
    This patch lets ioatdma driver set tcp_dma_copybreak value
    according to these results.

    Signed-off-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
    ---

    drivers/dma/dmaengine.c | 3 +++
    drivers/dma/ioat_dma.c | 15 +++++++++++++++
    include/linux/dmaengine.h | 2 ++
    3 files changed, 20 insertions(+), 0 deletions(-)

    diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
    index 97b329e..d57365a 100644
    --- a/drivers/dma/dmaengine.c
    +++ b/drivers/dma/dmaengine.c
    @@ -70,6 +70,7 @@ #include <linux/percpu.h>
    #include <linux/rcupdate.h>
    #include <linux/mutex.h>
    #include <linux/jiffies.h>
    +#include <net/tcp.h>

    static DEFINE_MUTEX(dma_list_mutex);
    static LIST_HEAD(dma_device_list);
    @@ -402,6 +403,8 @@ int dma_async_device_register(struct dma
    list_add_tail(&device->global_node, &dma_device_list);
    mutex_unlock(&dma_list_mutex);

    + sysctl_tcp_dma_copybreak = device->tcp_dma_copybreak;
    +
    dma_clients_notify_available();

    return 0;
    diff --git a/drivers/dma/ioat_dma.c b/drivers/dma/ioat_dma.c
    index 9c0b90a..42e5bfb 100644
    --- a/drivers/dma/ioat_dma.c
    +++ b/drivers/dma/ioat_dma.c
    @@ -53,6 +53,12 @@ #define WATCHDOG_DELAY round_jiffies(ms
    static void ioat_dma_chan_reset_part2(struct work_struct *work);
    static void ioat_dma_chan_watchdog(struct work_struct *work);

    +/*
    + * default tcp_dma_copybreak values for different IOAT versions
    + */
    +#define IOAT1_DEFAULT_TCP_DMA_COPYBREAK 4096
    +#define IOAT2_DEFAULT_TCP_DMA_COPYBREAK 2048
    +
    /* internal functions */
    static void ioat_dma_start_null_desc(struct ioat_dma_chan *ioat_chan);
    static void ioat_dma_memcpy_cleanup(struct ioat_dma_chan *ioat_chan);
    @@ -1571,6 +1577,15 @@ struct ioatdma_device *ioat_dma_probe(st
    if (err)
    goto err_self_test;

    + switch (device->version) {
    + case IOAT_VER_1_2:
    + device->common.tcp_dma_copybreak = IOAT1_DEFAULT_TCP_DMA_COPYBREAK;
    + break;
    + case IOAT_VER_2_0:
    + device->common.tcp_dma_copybreak = IOAT2_DEFAULT_TCP_DMA_COPYBREAK;
    + break;
    + }
    +
    dma_async_device_register(&device->common);

    INIT_DELAYED_WORK(&device->work, ioat_dma_chan_watchdog);
    diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
    index d08a5c5..c09128e 100644
    --- a/include/linux/dmaengine.h
    +++ b/include/linux/dmaengine.h
    @@ -251,6 +251,7 @@ struct dma_async_tx_descriptor {
    * @global_node: list_head for global dma_device_list
    * @cap_mask: one or more dma_capability flags
    * @max_xor: maximum number of xor sources, 0 if no capability
    + * @tcp_dma_copybreak: lower limit of TCP socket reads size offloaded by DMA
    * @refcount: reference count
    * @done: IO completion struct
    * @dev_id: unique device ID
    @@ -272,6 +273,7 @@ struct dma_device {
    struct list_head global_node;
    dma_cap_mask_t cap_mask;
    int max_xor;
    + int tcp_dma_copybreak;

    struct kref refcount;
    struct completion done;


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