Disable observers for Mage_Reports. Module can not be disabled completely because other modules rely on it.

performance-mage_reports.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
/**
 * Disable observers for Mage_Reports module.
 */
-->
<config>
    <frontend>
        <events>
            <!-- Disable Mage_Reports -->
            <catalog_product_compare_remove_product>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </catalog_product_compare_remove_product>
            <customer_login>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </customer_login>
            <customer_logout>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </customer_logout>
            <catalog_controller_product_view>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </catalog_controller_product_view>
            <sendfriend_product>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </sendfriend_product>
            <catalog_product_compare_add_product>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </catalog_product_compare_add_product>
            <catalog_product_compare_item_collection_clear>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </catalog_product_compare_item_collection_clear>
            <sales_quote_item_save_before>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </sales_quote_item_save_before>
            <wishlist_add_product>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </wishlist_add_product>
            <wishlist_share>
                <observers>
                    <reports>
                        <type>disabled</type>
                    </reports>
                </observers>
            </wishlist_share>
            <!-- /Disable Mage_Reports -->
        </events>
    </frontend>
</config>